Method and apparatus for lossless coding of video data

ABSTRACT

The present disclosure provides apparatuses and methods for performing lossless coding of a code tree unit (CTU). According to certain disclosed embodiments, the methods include: receiving a bitstream comprising a plurality of coding tree unit (CTUs) in a picture, and determining whether lossless coding is applied to the plurality of CTUs, based on a plurality of flags, respectively. The plurality of flags comprise a first flag associated with a first CTU. The method further includes: in response to a determination that lossless coding is applied to the first CTU, performing lossless coding to the first CTU.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure claims priority to U.S. Provisional ApplicationNo. 62/953,466, filed on Dec. 24, 2019, and U.S. provisional applicationNo. 62/959,220, filed on Jan. 10, 2020, both of which are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

The present disclosure generally relates to video processing, and moreparticularly, to methods and apparatuses for performing lossless codingof a code tree unit (CTU).

BACKGROUND

A video is a set of static pictures (or “frames”) capturing the visualinformation. To reduce the storage memory and the transmissionbandwidth, a video can be compressed before storage or transmission anddecompressed before display. The compression process is usually referredto as encoding and the decompression process is usually referred to asdecoding. There are various video coding formats which use standardizedvideo coding technologies, most commonly based on prediction, transform,quantization, entropy coding and in-loop filtering. The video codingstandards, such as the High Efficiency Video Coding (HEVC/H.265)standard, the Versatile Video Coding (VVC/H.266) standard AVS standards,specifying the specific video coding formats, are developed bystandardization organizations. With more and more advanced video codingtechnologies being adopted in the video standards, the coding efficiencyof the new video coding standards get higher and higher.

SUMMARY OF THE DISCLOSURE

In some embodiments, an exemplary video processing method includes:receiving a bitstream comprising a plurality of coding tree unit (CTUs)in a picture, and determining whether lossless coding is applied to theplurality of CTUs, based on a plurality of flags, respectively. Theplurality of flags comprise a first flag associated with a first CTU.The method further includes: in response to a determination thatlossless coding is applied to the first CTU, performing lossless codingto the first CTU.

In some embodiments, an exemplary video processing apparatus includes atleast one memory for storing instructions and at least one processor.The at least one processor is configured to execute the instructions tocause the apparatus to perform: receiving a bitstream comprising aplurality of coding tree unit (CTUs) in a picture, and determiningwhether lossless coding is applied to the plurality of CTUs, based on aplurality of flags, respectively. The plurality of flags comprise afirst flag associated with a first CTU. The at least one processor isconfigured to execute the instructions to cause the apparatus to furtherperform: in response to a determination that lossless coding is appliedto the first CTU, performing lossless coding to the first CTU.

In some embodiments, an exemplary non-transitory computer readablestorage medium stores a set of instructions. The set of instructions areexecutable by one or more processing devices to cause a video processingapparatus to perform: receiving a bitstream comprising a plurality ofcoding tree unit (CTUs) in a picture, and determining whether losslesscoding is applied to the plurality of CTUs, based on a plurality offlags, respectively. The plurality of flags comprise a first flagassociated with a first CTU. The set of instructions are executable byone or more processing devices to cause a video processing apparatus toperform: in response to a determination that lossless coding is appliedto the first CTU, performing lossless coding to the first CTU.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and various aspects of the present disclosure areillustrated in the following detailed description and the accompanyingfigures. Various features shown in the figures are not drawn to scale.

FIG. 1 is a schematic diagram illustrating structures of an examplevideo sequence, according to some embodiments of the present disclosure.

FIG. 2A is a schematic diagram illustrating an exemplary encodingprocess of a hybrid video coding system, consistent with embodiments ofthe disclosure.

FIG. 2B is a schematic diagram illustrating another exemplary encodingprocess of a hybrid video coding system, consistent with embodiments ofthe disclosure.

FIG. 3A is a schematic diagram illustrating an exemplary decodingprocess of a hybrid video coding system, consistent with embodiments ofthe disclosure.

FIG. 3B is a schematic diagram illustrating another exemplary decodingprocess of a hybrid video coding system, consistent with embodiments ofthe disclosure.

FIG. 4 is a block diagram of an exemplary apparatus for encoding ordecoding a video, according to some embodiments of the presentdisclosure.

FIG. 5 illustrates an exemplary Table 1 showing exemplary coding treeunit (CTU) syntax for signaling whether a CTU is coded in lossless mode,according to some embodiments of the present disclosure.

FIG. 6 illustrates an exemplary Table 2 showing exemplarysequence-parameter-set (SPS) syntax using syntax elementsps_ctu_lossless_present_flag, according to some embodiments of thepresent disclosure.

FIG. 7 illustrates an exemplary Table 3 showing exemplary CTU syntax forusing syntax element sps_ctu_lossless_present_flag, according to someembodiments of the present disclosure.

FIG. 8 illustrates an exemplary Table 4 showing exemplary slice_headersyntax of slice level lossless flag, according to some embodiments ofthe present disclosure.

FIG. 9 illustrates an exemplary Table 5 showing exemplarycoding_tree_unit syntax, according to some embodiments of the presentdisclosure.

FIG. 10 illustrates an exemplary Table 6 showing exemplary pictureheader syntax for picture level lossless coding, according to someembodiments of the present disclosure.

FIG. 11 illustrates an exemplary Table 7 showing exemplary slice headersyntax using pic_lossless_flag, according to some embodiments of thepresent disclosure.

FIG. 12 illustrates an exemplary Table 8 showing exemplary PPS syntaxusing pps_lossless_flag, according to some embodiments of the presentdisclosure.

FIG. 13 illustrates an exemplary Table 9 showing exemplary pictureheader syntax using pps_lossless_flag, according to some embodiments ofthe present disclosure.

FIG. 14 illustrates an exemplary Table 10 showing exemplary SPS syntaxtable sequence level lossless coding, according to some embodiments ofthe present disclosure.

FIG. 15 illustrates an exemplary Table 11 showing exemplarycoding_tree_unit syntax using CTU level residual coding flag, accordingto some embodiments of the present disclosure.

FIG. 16 illustrates an exemplary Table 12 showing exemplarytransform_unit syntax using CTU level residual coding flag, according tosome embodiments of the present disclosure.

FIG. 17 illustrates exemplary types of edges to which deblocking filterprocess is not applied, according to some embodiments of the presentdisclosure.

FIG. 18 illustrates an exemplary Table 13 showing exemplarycoding_tree_unit syntax for disabling sample adaptive offset (SAO),according to some embodiments of the present disclosure.

FIG. 19 illustrates an exemplary Table 14 showing exemplarycoding_tree_unit syntax for disabling adaptive loop filter (ALF),according to some embodiments of the present disclosure.

FIG. 20 illustrates an exemplary derivation of variable invLumaSample,according to some embodiments of the present disclosure.

FIG. 21 illustrates exemplary conditions to enable/disable chromaresidual scaling, according to some embodiments of the presentdisclosure.

FIG. 22 illustrates an exemplary Table 15 showing exemplary coding unitsyntax for disabling sub-block transform (SBT) for a lossless CTU,according to some embodiments of the present disclosure.

FIG. 23 illustrates an exemplary Table 16 showing exemplary coding unitsyntax for disabling multiple-transform selection (MTS) of a losslessCTU, according to some embodiments of the present disclosure.

FIG. 24 illustrates an exemplary Table 17 showing exemplary coding unitsyntax for disabling low frequency non-separable transform (LFNST) for alossless CTU, according to some embodiments of the present disclosure.

FIG. 25 illustrates an exemplary Table 18 showing exemplary transformunit syntax for disabling a joint_cr_cr mode, according to someembodiments of the present disclosure.

FIG. 26 illustrates an exemplary Table 19 showing exemplary coding unitsyntax for disabling Intra Subpartition (ISP) mode for a lossless CTU,according to some embodiments of the present disclosure.

FIG. 27 illustrates an exemplary Table 20 showing exemplary transformunit syntax for transform_skip_flag signaling, according to someembodiments of the present disclosure.

FIG. 28 illustrates a flowchart of an exemplary video processing method,according to some embodiments of the present disclosure.

FIG. 29 illustrates an exemplary Table 21 showing exemplary syntax forcontrolling llama mapping with chroma scaling (LMCS) at the CTB level,according to some embodiments of the present disclosure.

FIG. 30 illustrates an exemplary Table 22 showing exemplary slice headersyntax for signaling LMCS control flags, according to some embodimentsof the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings. The followingdescription refers to the accompanying drawings in which the samenumbers in different drawings represent the same or similar elementsunless otherwise represented. The implementations set forth in thefollowing description of exemplary embodiments do not represent allimplementations consistent with the invention. Instead, they are merelyexamples of apparatuses and methods consistent with aspects related tothe invention as recited in the appended claims. Particular aspects ofthe present disclosure are described in greater detail below. The termsand definitions provided herein control, if in conflict with termsand/or definitions incorporated by reference.

The Joint Video Experts Team (JVET) of the ITU-T Video Coding ExpertGroup (ITU-T VCEG) and the ISO/IEC Moving Picture Expert Group (ISO/IECMPEG) is currently developing the Versatile Video Coding (VVC/H.266)standard. The VVC standard is aimed at doubling the compressionefficiency of its predecessor, the High Efficiency Video Coding(HEVC/H.265) standard. In other words, VVC's goal is to achieve the samesubjective quality as HEVC/H.265 using half the bandwidth.

In order to achieve the same subjective quality as HEVC/H.265 using halfthe bandwidth, the JVET has been developing technologies beyond HEVCusing the joint exploration model (JEM) reference software. As codingtechnologies were incorporated into the JEM, the JEM achievedsubstantially higher coding performance than HEVC.

The VVC standard has been developed recent, and continues to includemore coding technologies that provide better compression performance.VVC is based on the same hybrid video coding system that has been usedin modern video compression standards such as HEVC, H.264/AVC, MPEG2,H.263, etc.

A video is a set of static pictures (or “frames”) arranged in a temporalsequence to store visual information. A video capture device (e.g., acamera) can be used to capture and store those pictures in a temporalsequence, and a video playback device (e.g., a television, a computer, asmartphone, a tablet computer, a video player, or any end-user terminalwith a function of display) can be used to display such pictures in thetemporal sequence. Also, in some applications, a video capturing devicecan transmit the captured video to the video playback device (e.g., acomputer with a monitor) in real-time, such as for surveillance,conferencing, or live broadcasting.

For reducing the storage space and the transmission bandwidth needed bysuch applications, the video can be compressed before storage andtransmission and decompressed before the display. The compression anddecompression can be implemented by software executed by a processor(e.g., a processor of a generic computer) or specialized hardware. Themodule for compression is generally referred to as an “encoder,” and themodule for decompression is generally referred to as a “decoder.” Theencoder and decoder can be collectively referred to as a “codec.” Theencoder and decoder can be implemented as any of a variety of suitablehardware, software, or a combination thereof. For example, the hardwareimplementation of the encoder and decoder can include circuitry, such asone or more microprocessors, digital signal processors (DSPs),application-specific integrated circuits (ASICs), field-programmablegate arrays (FPGAs), discrete logic, or any combinations thereof. Thesoftware implementation of the encoder and decoder can include programcodes, computer-executable instructions, firmware, or any suitablecomputer-implemented algorithm or process fixed in a computer-readablemedium. Video compression and decompression can be implemented byvarious algorithms or standards, such as MPEG-1, MPEG-2, MPEG-4, H.26xseries, or the like. In some applications, the codec can decompress thevideo from a first coding standard and re-compress the decompressedvideo using a second coding standard, in which case the codec can bereferred to as a “transcoder.”

The video encoding process can identify and keep useful information thatcan be used to reconstruct a picture and disregard unimportantinformation for the reconstruction. If the disregarded, unimportantinformation cannot be fully reconstructed, such an encoding process canbe referred to as “lossy.” Otherwise, it can be referred to as“lossless.” Most encoding processes are lossy, which is a tradeoff toreduce the needed storage space and the transmission bandwidth.

The useful information of a picture being encoded (referred to as a“current picture”) include changes with respect to a reference picture(e.g., a picture previously encoded and reconstructed). Such changes caninclude position changes, luminosity changes, or color changes of thepixels, among which the position changes are mostly concerned. Positionchanges of a group of pixels that represent an object can reflect themotion of the object between the reference picture and the currentpicture.

A picture coded without referencing another picture (i.e., it is its ownreference picture) is referred to as an “I-picture.” A picture codedusing a previous picture as a reference picture is referred to as a“P-picture.” A picture coded using both a previous picture and a futurepicture as reference pictures (i.e., the reference is “bi-directional”)is referred to as a “B-picture.”

FIG. 1 illustrates structures of an example video sequence 100,according to some embodiments of the present disclosure. Video sequence100 can be a live video or a video having been captured and archived.Video 100 can be a real-life video, a computer-generated video (e.g.,computer game video), or a combination thereof (e.g., a real-life videowith augmented-reality effects). Video sequence 100 can be inputted froma video capture device (e.g., a camera), a video archive (e.g., a videofile stored in a storage device) containing previously captured video,or a video feed interface (e.g., a video broadcast transceiver) toreceive video from a video content provider.

As shown in FIG. 1, video sequence 100 can include a series of picturesarranged temporally along a timeline, including pictures 102, 104, 106,and 108. Pictures 102-106 are continuous, and there are more picturesbetween pictures 106 and 108. In FIG. 1, picture 102 is an I-picture,the reference picture of which is picture 102 itself. Picture 104 is aP-picture, the reference picture of which is picture 102, as indicatedby the arrow. Picture 106 is a B-picture, the reference pictures ofwhich are pictures 104 and 108, as indicated by the arrows. In someembodiments, the reference picture of a picture (e.g., picture 104) canbe not immediately preceding or following the picture. For example, thereference picture of picture 104 can be a picture preceding picture 102.It should be noted that the reference pictures of pictures 102-106 areonly examples, and the present disclosure does not limit embodiments ofthe reference pictures as the examples shown in FIG. 1.

Typically, video codecs do not encode or decode an entire picture at onetime due to the computing complexity of such tasks. Rather, they cansplit the picture into basic segments, and encode or decode the picturesegment by segment. Such basic segments are referred to as basicprocessing units (“BPUs”) in the present disclosure. For example,structure 110 in FIG. 1 shows an example structure of a picture of videosequence 100 (e.g., any of pictures 102-108). In structure 110, apicture is divided into 4×4 basic processing units, the boundaries ofwhich are shown as dash lines. In some embodiments, the basic processingunits can be referred to as “macroblocks” in some video coding standards(e.g., MPEG family, H.261, H.263, or H.264/AVC), or as “coding treeunits” (“CTUs”) in some other video coding standards (e.g., H.265/HEVCor H.266/VVC). The basic processing units can have variable sizes in apicture, such as 128×128, 64×64, 32>32, 16×16, 4×8, 16×32, or anyarbitrary shape and size of pixels. The sizes and shapes of the basicprocessing units can be selected for a picture based on the balance ofcoding efficiency and levels of details to be kept in the basicprocessing unit.

The basic processing units can be logical units, which can include agroup of different types of video data stored in a computer memory(e.g., in a video frame buffer). For example, a basic processing unit ofa color picture can include a luma component (Y) representing achromaticbrightness information, one or more chroma components (e.g., Cb and Cr)representing color information, and associated syntax elements, in whichthe luma and chroma components can have the same size of the basicprocessing unit. The luma and chroma components can be referred to as“coding tree blocks” (“CTBs”) in some video coding standards (e.g.,H.265/HEVC or H.266/VVC). Any operation performed to a basic processingunit can be repeatedly performed to each of its luma and chromacomponents.

Video coding has multiple stages of operations, examples of which areshown in FIGS. 2A-2B and FIGS. 3A-3B. For each stage, the size of thebasic processing units can still be too large for processing, and thuscan be further divided into segments referred to as “basic processingsub-units” in the present disclosure, in some embodiments, the basicprocessing s units can be referred to as “blocks” in some video codingstandards (e.g., MPEG family, H.261, H.263, or H.264/AVC), or as “codingunits” (“CUs”) in some other video coding standards (e.g., H.265/HEVC orH.266/VVC). A basic processing sub-unit can have the same or smallersize than the basic processing unit. Similar to the basic processingunits, basic processing sub-units are also logical units, which caninclude a group of different types of video data (e.g., Y, Cb, Cr, andassociated syntax elements) stored in a computer memory (e.g., in avideo frame buffer). Any operation performed to a basic processingsub-unit can be repeatedly performed to each of its lura and chromacomponents. It should be noted that such division can be performed tofurther levels depending on processing needs. It should also be notedthat different stages can divide the basic processing units usingdifferent schemes.

For example, at a mode decision stage (an example of which is shown inFIG. 2B), the encoder can decide what prediction mode (e.g.,intra-picture prediction or inter-picture prediction) to use for a basicprocessing unit, which can be too large to make such a decision. Theencoder can split the basic processing unit into multiple basicprocessing sub-units (e.g., CUs as in H.265/HEVC or H.266/VVC), anddecide a prediction type for each individual basic processing sub-unit.

For another example, at a prediction stage (an example of which is shownin FIGS. 2A-2B), the encoder can perform prediction operation at thelevel of basic processing sub-units (e.g., CUs). However, in some cases,a basic processing sub-unit can still be too large to process. Theencoder can further split the basic processing sub-unit into smallersegments (e.g., referred to as “prediction blocks” or “PBs” inH.265/HEVC or H.266/VVC), at the level of which the prediction operationcan be performed.

For another example, at a transform stage (an example of which is shownin FIGS. 2A-2B), the encoder can perform a transform operation forresidual basic processing sub-units (e.g., CUs). However, in some cases,a basic processing sub-unit can still be too large to process. Theencoder can further split the basic processing sub-unit into smallersegments (e.g., referred to as “transform blocks” or “TBs” in H.265/HEVCor H266/VVC), at the level of which the transform operation can beperformed. It should be noted that the division schemes of the samebasic processing sub-unit can be different at the prediction stage andthe transform stage. For example, in H.265/HEVC or H266/VVC, theprediction blocks and transform blocks of the same CU can have differentsizes and numbers.

In structure 110 of FIG. 1, basic processing unit 112 is further dividedinto 3×3 basic processing sub-units, the boundaries of which are shownas dotted lines. Different basic processing units of the same picturecan be divided into basic processing sub-units in different schemes.

In some implementations, to provide the capability of parallelprocessing and error resilience to video encoding and decoding, apicture can be divided into regions for processing, such that, for aregion of the picture, the encoding or decoding process can depend on noinformation from any other region of the picture. In other words, eachregion of the picture can be processed independently. By doing so, thecodec can process different regions of a picture in parallel, thusincreasing the coding efficiency. Also, when data of a region iscorrupted in the processing or lost in network transmission, the codeccan correctly encode or decode other regions of the same picture withoutreliance on the corrupted or lost data, thus providing the capability oferror resilience. In some video coding standards, a picture can bedivided into different types of regions. For example, H.265/HEVC andH.266/VVC provide two types of regions: “slices” and “tiles.” It shouldalso be noted that different pictures of video sequence 100 can havedifferent partition schemes for dividing a picture into regions.

For example, in FIG. 1, structure 110 is divided into three regions 114,116, and 118, the boundaries of which are shown as solid lines insidestructure 110. Region 114 includes four basic processing units. Each ofregions 116 and 118 includes six basic processing units. It should benoted that the basic processing units, basic processing sub-units, andregions of structure 110 in FIG. 1 are only examples, and the presentdisclosure does not limit embodiments thereof.

FIG. 2A illustrates a schematic diagram of an example encoding process200A, consistent with embodiments of the disclosure. For example, theencoding process 200A can be performed by an encoder. As shown in FIG.2A, the encoder can encode video sequence 202 into video bitstream 228according to process 200A. Similar to video sequence 100 in FIG. 1,video sequence 202 can include a set of pictures (referred to as“original pictures”) arranged in a temporal order. Similar to structure110 in FIG. 1, each original picture of video sequence 202 can bedivided by the encoder into basic processing units, basic processingsub-units, or regions for processing. In some embodiments, the encodercan perform process 200A at the level of basic processing units for eachoriginal picture of video sequence 202. For example, the encoder canperform process 200A in an iterative manner, in which the encoder canencode a basic processing unit in one iteration of process 200A. In someembodiments, the encoder can perform process 200A in parallel forregions (e.g., regions 114-118) of each original picture of videosequence 202.

In FIG. 2A, the encoder can feed a basic processing unit (referred to asan “original BPU”) of an original picture of video sequence 202 toprediction stage 204 to generate prediction data 206 and predicted BPU208. The encoder can subtract predicted BPU 208 from the original BPU togenerate residual BPU 210. The encoder can feed residual BPU 210 totransform stage 212 and quantization stage 214 to generate quantizedtransform coefficients 216. The encoder can feed prediction data 206 andquantized transform coefficients 216 to binary coding stage 226 togenerate video bitstream 228. Components 202, 204, 206, 208, 210, 212,214, 216, 226, and 228 can be referred to as a “forward path.” Duringprocess 200A, after quantization stage 214, the encoder can feedquantized transform coefficients 216 to inverse quantization stage 218and inverse transform stage 220 to generate reconstructed residual BPU222. The encoder can add reconstructed residual BPU 222 to predicted BPU208 to generate prediction reference 224, which is used in predictionstage 204 for the next iteration of process 200A. Components 218, 220,222, and 224 of process 200A can be referred to as a “reconstructionpath.” The reconstruction path can be used to ensure that both theencoder and the decoder use the same reference data for prediction.

The encoder can perform process 200A iteratively to encode each originalBPU of the original picture (in the forward path) and generate predictedreference 224 for encoding the next original BPU of the original picture(in the reconstruction path). After encoding all original BPUs of theoriginal picture, the encoder can proceed to encode the next picture invideo sequence 202.

Referring to process 200A, the encoder can receive video sequence 202generated by a video capturing device (e.g., a camera). The term“receive” used herein can refer to receiving, inputting, acquiring,retrieving, obtaining, reading, accessing, or any action in any mannerfor inputting data.

At prediction stage 204, at a current iteration, the encoder can receivean original BPU and prediction reference 224, and perform a predictionoperation to generate prediction data 206 and predicted BPU 208.Prediction reference 224 can be generated from the reconstruction pathof the previous iteration of process 200A. The purpose of predictionstage 204 is to reduce information redundancy by extracting predictiondata 206 that can be used to reconstruct the original BPU as predictedBPU 208 from prediction data 206 and prediction reference 224.

Ideally, predicted BPU 208 can be identical to the original BPU.However, due to non-ideal prediction and reconstruction operations,predicted BPU 208 is generally slightly different from the original BPU.For recording such differences, after generating predicted BPU 208, theencoder can subtract it from the original BPU to generate residual BPU210. For example, the encoder can subtract values (e.g., greyscalevalues or RGB values) of pixels of predicted BPU 208 from values ofcorresponding pixels of the original BPU. Each pixel of residual BPU 210can have a residual value as a result of such subtraction between thecorresponding pixels of the original BPU and predicted BPU 208. Comparedwith the original BPU, prediction data 206 and residual BPU 210 can havefewer bits, but they can be used to reconstruct the original BPU withoutsignificant quality deterioration. Thus, the original BPU is compressed.

To further compress residual BPU 210, at transform stage 212, theencoder can reduce spatial redundancy of residual BPU 210 by decomposingit into a set of two-dimensional “base patterns,” each base patternbeing associated with a “transform coefficient.” The base patterns canhave the same size (e.g., the size of residual BPU 210). Each basepattern can represent a variation frequency (e.g., frequency ofbrightness variation) component of residual BPU 210. None of the basepatterns can be reproduced from any combinations (e.g., linearcombinations) of any other base patterns. In other words, thedecomposition can decompose variations of residual BPU 210 into afrequency domain. Such a decomposition is analogous to a discreteFourier transform of a function, in which the base patterns areanalogous to the base functions (e.g., trigonometry functions) of thediscrete Fourier transform, and the transform coefficients are analogousto the coefficients associated with the base functions.

Different transform algorithms can use different base patterns. Varioustransform algorithms can be used at transform stage 212, such as, forexample, a discrete cosine transform, a discrete sine transform, or thelike. The transform at transform stage 212 is invertible. That is, theencoder can restore residual BPU 210 by an inverse operation of thetransform (referred to as an “inverse transform”). For example, torestore a pixel of residual BPU 210, the inverse transform can bemultiplying values of corresponding pixels of the base patterns byrespective associated coefficients and adding the products to produce aweighted sum. For a video coding standard, both the encoder and decodercan use the same transform algorithm (thus the same base patterns).Thus, the encoder can record only the transform coefficients, from whichthe decoder can reconstruct residual BPU 210 without receiving the basepatterns from the encoder. Compared with residual BPU 210, the transformcoefficients can have fewer bits, but they can be used toreconstructresidual BPU 210 without significant quality deterioration.Thus, residual BPU 210 is further compressed.

The encoder can further compress the transform coefficients atquantization stage 214. In the transform process, different basepatterns can represent different variation frequencies (e.g., brightnessvariation frequencies). Because human eyes are generally better atrecognizing low-frequency variation, the encoder can disregardinformation of high-frequency variation without causing significantquality deterioration in decoding. For example, at quantization stage214, the encoder can generate quantized transform coefficients 216 bydividing each transform coefficient by an integer value (referred to asa “quantization parameter”) and rounding the quotient to its nearestinteger. After such an operation, some transform coefficients of thehigh-frequency base patterns can be converted to zero, and the transformcoefficients of the low-frequency base patterns can be converted tosmaller integers. The encoder can disregard the zero-value quantizedtransform coefficients 216, by which the transform coefficients arefurther compressed. The quantization process is also invertible, inwhich quantized transform coefficients 216 can be reconstructed to thetransform coefficients in an inverse operation of the quantization(referred to as “inverse quantization”).

Because the encoder disregards the remainders of such divisions in therounding operation, quantization stage 214 can be loss-. Typically,quantization stage 214 can contribute the most information loss inprocess 200A. The larger the information loss is, the fewer bits thequantized transform coefficients 216 can need. For obtaining differentlevels of information loss, the encoder can use different values of thequantization parameter or any other parameter of the quantizationprocess.

At binary coding stage 226, the encoder can encode prediction data 206and quantized transform coefficients 216 using a binary codingtechnique, such as, for example, entropy coding, variable length coding,arithmetic coding, Huffman coding, context-adaptive binary arithmeticcoding, or any other lossless or lossy compression algorithm. In someembodiments, besides prediction data 206 and quantized transformcoefficients 216, the encoder can encode other information at binarycoding stage 226, such as, for example, a prediction mode used atprediction stage 204, parameters of the prediction operation, atransform type at transform stage 212, parameters of the quantizationprocess (e.g., quantization parameters), an encoder control parameter(e.g., a bitrate control parameter), or the like. The encoder can usethe output data of binary coding stage 226 to generate video bitstream228. In some embodiments, video bitstream 228 can be further packetizedfor network transmission.

Referring to the reconstruction path of process 200A, at inversequantization stage 218, the encoder can perform inverse quantization onquantized transform coefficients 216 to generate reconstructed transformcoefficients. At inverse transform stage 220, the encoder can generatereconstructed residual BPU 222 based on the reconstructed transformcoefficients. The encoder can add reconstructed residual BPU 222 topredicted BPU 208 to generate prediction reference 224 that is to beused in the next iteration of process 200A.

It should be noted that other variations of the process 200A can be usedto encode video sequence 202. In some embodiments, stages of process200A can be performed by the encoder in different orders. In someembodiments, one or more stages of process 200A can be combined into asingle stage. In some embodiments, a single stage of process 200A can bedivided into multiple stages. For example, transform stage 212 andquantization stage 214 can be combined into a single stage. In someembodiments, process 200A can include additional stages. In someembodiments, process 200A can omit one or more stages in FIG. 2A.

FIG. 2B illustrates a schematic diagram of another example encodingprocess 200B, consistent with embodiments of the disclosure. Process200B can be modified from process 200A. For example, process 200B can beused by an encoder conforming to a hybrid video coding standard (e.g.,H.26x series). Compared with process 200A, the forward path of process200B additionally includes mode decision stage 230 and dividesprediction stage 204 into spatial prediction stage 2042 and temporalprediction stage 2044. The reconstruction path of process 200Badditionally includes loop filter stage 232 and buffer 234.

Generally, prediction techniques can be categorized into two types:spatial prediction and temporal prediction. Spatial prediction (e.g., anintra-picture prediction or “intra prediction”) can use pixels from oneor more already coded neighboring BPUs in the same picture to predictthe current BPU. That is, prediction reference 224 in the spatialprediction can include the neighboring BPUs. The spatial prediction canreduce the inherent spatial redundancy of the picture. Temporalprediction (e.g., an inter-picture prediction or “inter prediction”) canuse regions from one or more already coded pictures to predict thecurrent BPU. That is, prediction reference 224 in the temporalprediction can include the coded pictures. The temporal prediction canreduce the inherent temporal redundancy of the pictures.

Referring to process 200B, in the forward path, the encoder performs theprediction operation at spatial prediction stage 2042 and temporalprediction stage 2044, For example, at spatial prediction stage 2042,the encoder can perform the intra prediction. For an original BPU of apicture being encoded, prediction reference 224 can include one or moreneighboring BPUs that have been encoded (in the forward path) andreconstructed (in the reconstructed path) in the same picture. Theencoder can generate predicted BPU 208 by extrapolating the neighboringBPUs. The extrapolation technique can include, for example, a linearextrapolation or interpolation, a polynomial extrapolation orinterpolation, or the like in some embodiments, the encoder can performthe extrapolation at the pixel level, such as by extrapolating values ofcorresponding pixels for each pixel of predicted BPU 208. Theneighboring BPUs used for extrapolation can be located with respect tothe original BPU from various directions, such as in a verticaldirection (e.g., on top of the original BPU), a horizontal direction(e.g., to the left of the original BPU), a diagonal direction (e.g., tothe down-left, down-right, up-left, or up-right of the original BPU), orany direction defined in the used video coding standard. For the intraprediction, prediction data 206 can include, for example, locations(e.g., coordinates) of the used neighboring BPUs, sizes of the usedneighboring BPUs, parameters of the extrapolation, a direction of theused neighboring BPUs with respect to the original BPU, or the like.

For another example, at temporal prediction stage 2044, the encoder canperform the inter prediction. For an original BPU of a current picture,prediction reference 224 can include one or more pictures (referred toas “reference pictures”) that have been encoded (in the forward path)and reconstructed (in the reconstructed path). In some embodiments, areference picture can be encoded and reconstructed BPU by BPU. Forexample, the encoder can add reconstructed residual BPU 222 to predictedBPU 208 to generate a reconstructed BPU. When all reconstructed BPUs ofthe same picture are generated, the encoder can generate a reconstructedpicture as a reference picture. The encoder can perform an operation of“motion estimation” to search for a matching region in a scope (referredto as a “search window”) of the reference picture. The location of thesearch window in the reference picture can be determined based on thelocation of the original BPU in the current picture. For example, thesearch window can be centered at a location having the same coordinatesin the reference picture as the original BPU in the current picture andcan be extended out for a predetermined distance. When the encoderidentifies (e.g., by using a pel-recursive algorithm, a block-matchingalgorithm, or the like) a region similar to the original BPU in thesearch window, the encoder can determine such a region as the matchingregion. The matching region can have different dimensions (e.g., beingsmaller than, equal to, larger than, or in a different shape) from theoriginal BPU. Because the reference picture and the current picture aretemporally separated in the timeline (e.g., as shown in FIG. 1), it canbe deemed that the matching region “moves” to the location of theoriginal BPU as time goes by. The encoder can record the direction anddistance of such a motion as a “motion vector.” When multiple referencepictures are used (e.g., as picture 106 in FIG. 1), the encoder cansearch for a matching region and determine its associated motion vectorfor each reference picture. In some embodiments, the encoder can assignweights to pixel values of the matching regions of respective matchingreference pictures.

The motion estimation can be used to identify various types of motions,such as, for example, translations, rotations, zooming, or the like. Forinter prediction, prediction data 206 can include, for example,locations (e.g., coordinates) of the matching region, the motion vectorsassociated with the matching region, the number of reference pictures,weights associated with the reference pictures, or the like.

For generating predicted BPU 208, the encoder can perform an operationof “motion compensation.” The motion compensation can be used toreconstruct predicted BPU 208 based on prediction data 206 (e.g., themotion vector) and prediction reference 224. For example, the encodercan move the matching region of the reference picture according to themotion vector, in which the encoder can predict the original BPU of thecurrent picture. When multiple reference pictures are used (e.g., aspicture 106 in FIG. 1), the encoder can move the matching regions of thereference pictures according to the respective motion vectors andaverage pixel values of the matching regions. In some embodiments, ifthe encoder has assigned weights to pixel values of the matching regionsof respective matching reference pictures, the encoder can add aweighted sum of the pixel values of the moved matching regions.

In some embodiments, the inter prediction can be unidirectional orbidirectional. Unidirectional inter predictions can use one or morereference pictures in the same temporal direction with respect to thecurrent picture. For example, picture 104 in FIG. 1 is a unidirectionalinter-predicted picture, in which the reference picture (i.e., picture102) precedes picture 104. Bidirectional inter predictions can use oneor more reference pictures at both temporal directions with respect tothe current picture. For example, picture 106 in FIG. 1 is abidirectional inter-predicted picture, in which the reference pictures(i.e., pictures 104 and 108) are at both temporal directions withrespect to picture 104.

Still referring to the forward path of process 200B, after spatialprediction 2042 and temporal prediction stage 2044, at mode decisionstage 230, the encoder can select a prediction mode (one of the intraprediction or the inter prediction) for the current iteration of process200B. For example, the encoder can perform a rate-distortionoptimization technique, in which the encoder can select a predictionmode to minimize a value of a cost function depending on a bit rate of acandidate prediction mode and distortion of the reconstructed referencepicture under the candidate prediction mode. Depending on the selectedprediction mode, the encoder can generate the corresponding predictedBPU 208 and predicted data 206.

In the reconstruction path of process 200B, if intra prediction mode hasbeen selected in the forward path, after generating prediction reference224 (e.g., the current BPU that has been encoded and reconstructed inthe current picture), the encoder can directly feed prediction reference224 to spatial prediction stage 2042 for later usage (e.g., forextrapolation of a next BPU of the current picture). If the interprediction mode has been selected in the forward path, after generatingprediction reference 224 (e.g., the current picture in which all BPUshave been encoded and reconstructed), the encoder can feed predictionreference 224 to loop filter stage 232, at which the encoder can apply aloop filter to prediction reference 224 to reduce or eliminatedistortion (e.g., blocking artifacts) introduced by the interprediction. The encoder can apply various loop filter techniques at loopfilter stage 232, such as, for example, deblocking, sample adaptiveoffsets, adaptive loop filters, or the like. The loop-filtered referencepicture can be stored in buffer 234 (or “decoded picture buffer”) forlater use (e.g., to be used as an inter-prediction reference picture fora future picture of video sequence 202). The encoder can store one ormore reference pictures in buffer 234 to be used at temporal predictionstage 2044. In some embodiments, the encoder can encode parameters ofthe loop filter (e.g., a loop filter strength) at binary coding stage226, along with quantized transform coefficients 216, prediction data206, and other information.

FIG. 3A illustrates a schematic diagram of an example decoding process300A, consistent with embodiments of the disclosure. Process 300A can bea decompression process corresponding to the compression process 200A inFIG. 2A. In some embodiments, process 300A can be similar to thereconstruction path of process 200A. A decoder can decode videobitstream 228 into video stream 304 according to process 300A. Videostream 304 can be very similar to video sequence 202. However, due tothe information loss in the compression and decompression process (e.g.,quantization stage 214 in FIGS. 2A-2B), generally, video stream 304 isnot identical to video sequence 202. Similar to processes 200A and 200Bin FIGS. 2A-2B, the decoder can perform process 300A at the level ofbasic processing units (BPUs) for each picture encoded in videobitstream 228. For example, the decoder can perform process 300A in aniterative manner, in which the decoder can decode a basic processingunit in one iteration of process 300A. In some embodiments, the decodercan perform process 300A in parallel for regions (e.g., regions 114-118)of each picture encoded in video bitstream 228.

In FIG. 3A, the decoder can feed a portion of video bitstream 228associated with a basic processing unit (referred to as an “encodedBPU”) of an encoded picture to binary decoding stage 302. At binarydecoding stage 302, the decoder can decode the portion into predictiondata 206 and quantized transform coefficients 216. The decoder can feedquantized transform coefficients 216 to inverse quantization stage 218and inverse transform stage 220 to generate reconstructed residual BPU222. The decoder can feed prediction data 206 to prediction stage 204 togenerate predicted BPU 208. The decoder can add reconstructed residualBPU 222 to predicted BPU 208 to generate predicted reference 224. Insome embodiments, predicted reference 224 can be stored in a buffer(e.g., a decoded picture buffer in a computer memory). The decoder canfeed predicted reference 224 to prediction stage 204 for performing aprediction operation in the next iteration of process 300A.

The decoder can perform process 300A iteratively to decode each encodedBPU of the encoded picture and generate predicted reference 224 forencoding the next encoded BPU of the encoded picture. After decoding allencoded BPUs of the encoded picture, the decoder can output the pictureto video stream 304 for display and proceed to decode the next encodedpicture in video bitstream 228.

At binary decoding stage 302, the decoder can perform an inverseoperation of the binary coding technique used by the encoder (e.g.,entropy coding, variable length coding, arithmetic coding, Huffmancoding, context-adaptive binary arithmetic coding, or any other losslesscompression algorithm). In some embodiments, besides prediction data 206and quantized transform coefficients 216, the decoder can decode otherinformation at binary decoding stage 302, such as, for example, aprediction mode, parameters of the prediction operation, a transformtype, parameters of the quantization process (e.g., quantizationparameters), an encoder control parameter (e.g., a bitrate controlparameter), or the like. In some embodiments, if video bitstream 228 istransmitted over a network in packets, the decoder can depacketize videobitstream 228 before feeding it to binary decoding stage 302.

FIG. 3B illustrates a schematic diagram of another example decodingprocess 300B, consistent with embodiments of the disclosure. Process300B can be modified from process 300A. For example, process 300B can beused by a decoder conforming to a hybrid video coding standard (e.g.,H.26x series). Compared with process 300A, process 300B additionallydivides prediction stage 204 into spatial prediction stage 2042 andtemporal prediction stage 2044, and additionally includes loop filterstage 232 and buffer 234.

In process 300B, for an encoded basic processing unit (referred to as a“current BPU”) of an encoded picture (referred to as a “currentpicture”) that is being decoded, prediction data 206 decoded from binarydecoding stage 302 by the decoder can include various types of data,depending on what prediction mode was used to encode the current BPU bythe encoder. For example, if intra prediction was used by the encoder toencode the current BPU, prediction data 206 can include a predictionmode indicator (e.g., a flag value) indicative of the intra prediction,parameters of the intra prediction operation, or the like. Theparameters of the intra prediction operation can include, for example,locations (e.g., coordinates) of one or more neighboring BPUs used as areference, sizes of the neighboring BPUs, parameters of extrapolation, adirection of the neighboring BPUs with respect to the original BPU, orthe like. For another example, if inter prediction was used by theencoder to encode the current BPU, prediction data 206 can include aprediction mode indicator (e.g., a flag value) indicative of the interprediction, parameters of the inter prediction operation, or the like.The parameters of the inter prediction operation can include, forexample, the number of reference pictures associated with the currentBPU, weights respectively associated with the reference pictures,locations (e.g., coordinates) of one or more matching regions in therespective reference pictures, one or more motion vectors respectivelyassociated with the matching regions, or the like.

Based on the prediction mode indicator, the decoder can decide whetherto perform a spatial prediction (e.g., the intra prediction) at spatialprediction stage 2042 or a temporal prediction (e.g., the interprediction) at temporal prediction stage 2044. The details of performingsuch spatial prediction or temporal prediction are described in FIG. 2Band will not be repeated hereinafter. After performing such spatialprediction or temporal prediction, the decoder can generate predictedBPU 208. The decoder can add predicted BPU 208 and reconstructedresidual BPU 222 to generate prediction reference 224, as described inFIG. 3A.

In process 300B, the decoder can feed predicted reference 224 to spatialprediction stage 2042 or temporal prediction stage 2044 for performing aprediction operation in the next iteration of process 300B. For example,if the current BPU is decoded using the intra prediction at spatialprediction stage 2042, after generating prediction reference 224 (e.g.,the decoded current BPU), the decoder can directly feed predictionreference 224 to spatial prediction stage 2042 for later usage (e.g.,for extrapolation of a next BPU of the current picture) If the currentBPU is decoded using the inter prediction at temporal prediction stage2044, after generating prediction reference 224 (e.g., a referencepicture in which all BPU have been decoded), the encoder can feedprediction reference 224 to loop filter stage 232 to reduce or eliminatedistortion (e.g., blocking artifacts). The decoder can apply a loopfilter to prediction reference 224, in a way as described in FIG. 2B.The loop-filtered reference picture can be stored in buffer 234 (e.g., adecoded picture buffer in a computer memory) for later use (e.g., to beused as an inter-prediction reference picture for a future encodedpicture of video bitstream 228). The decoder can store one or morereference pictures in buffer 234 to be used at temporal prediction stage2044. In some embodiments, when the prediction mode indicator ofprediction data 206 indicates that inter prediction was used to encodethe current BPU, prediction data can further include parameters of theloop filter (e.g., a loop filter strength).

FIG. 4 is a block diagram of an example apparatus 400 for encoding ordecoding a video, consistent with embodiments of the disclosure. Asshown in FIG. 4, apparatus 400 can include processor 402. When processor402 executes instructions described herein, apparatus 400 can become aspecialized machine for video encoding or decoding. Processor 402 can beany type of circuitry capable of manipulating or processing information.For example, processor 402 can include any combination of any number ofa central processing unit (or “CPU”), a graphics processing unit (or“GPU”), a neural processing unit (“ITU”), a microcontroller unit(“MCU”), an optical processor, a programmable logic controller, amicrocontroller, a microprocessor, a digital signal processor, anintellectual property (IP) core, a Programmable bogie Array (PIA), aProgrammable Array Logic (PAL), a Generic Array Logic (GAL), a ComplexProgrammable Logic Device (CPLD), a Field-Programmable Gate Array(FPGA), a System On Chip (SoC), an Application-Specific IntegratedCircuit (ASIC), or the like. In some embodiments, processor 402 can alsobe a set of processors grouped as a single logical component. Forexample, as shown in FIG. 4, processor 402 can include multipleprocessors, including processor 402 a, processor 402 b, and processor402 n.

Apparatus 400 can also include memory 404 configured to store data(e.g., a set of instructions, computer codes, intermediate data, or thelike). For example, as shown in FIG. 4, the stored data can includeprogram instructions (e.g., program instructions for implementing thestages in processes 200A, 200B, 300A, or 300B) and data for processing(e.g., video sequence 202, video bitstream 228, or video stream 304).Processor 402 can access the program instructions and data forprocessing (e.g., via bus 410), and execute the program instructions toperform an operation or manipulation on the data for processing. Memory404 can include a high-speed random-access storage device or anon-volatile storage device. In some embodiments, memory 404 can includeany combination of any number of a random-access memory (RAM), aread-only memory (ROM), an optical disc, a magnetic disk, a hard drive,a solid-state drive, a flash drive, a security digital (SD) card, amemory stick, a compact flash (CF) card, or the like. Memory 404 canalso be a group of memories (not shown in FIG. 4) grouped as a singlelogical component.

Bus 410 can be a communication device that transfers data betweencomponents inside apparatus 400, such as an internal bus (e.g., aCPU-memory bus), an external bus (e.g., a universal serial bus port, aperipheral component interconnect express port or the like.

For ease of explanation without causing ambiguity, processor 402 andother data processing circuits are collectively referred to as a “dataprocessing circuit” in this disclosure. The data processing circuit canbe implemented entirely as hardware, or as a combination of software,hardware, or firmware. In addition, the data processing circuit can be asingle independent module or can be combined entirely or partially intoany other component of apparatus 400.

Apparatus 400 can further include network interface 406 to provide wiredor wireless communication with a network (e.g., the Internet, anintranet, a local area network, a mobile communications network, or thelike). In some embodiments, network interface 406 can include anycombination of any number of a network interface controller (NIC), aradio frequency (RF) module, a transponder, a transceiver, a modem, arouter, a gateway, a wired network adapter, a wireless network adapter,a Bluetooth adapter, an infrared adapter, an near-field communication(“NFC”) adapter, a cellular network chip, or the like.

In some embodiments, optionally, apparatus 400 can further includeperipheral interface 408 to provide a connection to one or moreperipheral devices. As shown in FIG. 4, the peripheral device caninclude, but is not limited to, a cursor control device (e.g., a mouse,a touchpad, or a touchscreen), a keyboard, a display (e.g., acathode-ray tube display, a liquid crystal display, or a light-emittingdiode display), a video input device (e.g., a camera or an inputinterface coupled to a video archive), or the like.

It should be noted that video codecs (e.g., a codec performing process200A, 200B, 300A, or 300B) can be implemented as any combination of anysoftware or hardware modules in apparatus 400. For example, some or allstages of process 200A, 200B, 300A, or 300B can be implemented as one ormore software modules of apparatus 400, such as program instructionsthat can be loaded into memory 404. For another example, some or allstages of process 200A, 200B, 300A, or 300B can be implemented as one ormore hardware modules of apparatus 400, such as a specialized dataprocessing circuit (e.g., an FPGA, an ASIC, an NPU, or the like).

In the quantization and inverse quantization functional blocks (e.g.,quantization 214 and inverse quantization 218 of FIG. 2A or FIG. 2B,inverse quantization 218 of FIG. 3A or FIG. 3B), a quantizationparameter (QP) is used to determine the amount of quantization (andinverse quantization) applied to the prediction residuals. Initial QPvalues used for coding of a picture or slice may be signaled at the highlevel, for example, using init_qp_minus26_syntax element in the PictureParameter Set (PPS) and using slice_qp_delta syntax element in the sliceheader. Further, the QP values may be adapted at the local level foreach CU using delta QP values sent at the granularity of quantizationgroups.

According to some embodiments, lossless coding can be achieved atsequence level by selecting the transform-skip mode for all of thecoding blocks. In order to achieve the lossless coding at sequencelevel, several coding tools need to be configured as the following:

-   -   Set maximum transform size to 32×32    -   Enable chroma transform skip    -   Disable dependent quantization    -   Disable sub-block transform (SBT)    -   Disables lura mapping with chroma scaling (LMCS)    -   Disables de-blocking filer (DF)    -   Disables sample adaptive offset (SAO)    -   Disables adaptive loop filter (ALF)    -   Disable multiple-transform selection (NITS)    -   Disable low frequency non-separable transform (LFNST)    -   Disable joint Cb-Cr mode    -   InternalBitDepth=0 (Input=Internal Bit Depth)

However, in the current design of lossless coding of VVC 7, the abovecoding tools are configured at sequence level, and thus the codingefficiency is compromised in mixed coding scenario where one part of theimage is coded as lossless mode and another part of the image is codedas lossy mode.

To achieve efficient compression in mixed coding (e.g., lossy andlossless coding) scenario, the present disclosure provides methods thatsignal a flag for each coding tree unit (CTU) of an image frame toindicate whether the CTU is coded in in a lossless mode or a lossy mode.

According to some embodiments, a CTU level lossless flag can be used tosignal whether lossless coding is applied to a CTU. Specifically, a flagis signaled at each CTU to indicate if the CTU is coded as lossless modeor not. The following are the semantics of the disclosed CTU levellossless flag, consistent with the present embodiments:

ctu_lossless_flag[ xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] equalto 1 specifies that the coding tree unit at luma location ( xCtb, yCtb )is losslessly coded. ctu_losslessflag[ xCtb >> CtbLog2SizeY ][ yCtb >>CtbLog2SizeY ] equal to 0 specifies that the coding tree unit at lumalocation ( xCtb, yCtb ) is not coded as lossless mode. Whenctu_lossless_flag[ xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] is notpresent, it is inferred to be equal to 0. The variable CtbLog2SizeY isderived as: folCtbLog2SizeY = sps_log2_ctu_size_minus5 + 5.

FIG. 5 illustrates an exemplary Table 1 showing exemplary CTU syntax forsignaling whether a CTU is coded in lossless mode, according to someembodiments of the present disclosure. Referring to Table 1, the CTUlevel lossless flag (e.g., ctu_lossless_flag[CtbAddrX][CtbAddrY]) issignaled at the beginning of each CTU. The italicized syntax elements inbox 501 show the difference of the proposed method with current VVC 7syntax table.

According to some embodiments, an SPS level flag is signaled to indicatewhether the CTU level lossless flags are present in the bit-stream ornot. The following are the semantics of the disclosed SPS flag,consistent with the present embodiments:

sps_ctu_lossless_present_flag equal to 1 specifies thatctu_lossless_flag is present in the bitstream. Ifsps_ctu_lossless_present_flag is equal to 1,sps_transform_skip_enabled_flag is inferred to be 1.sps_ctu_lossless_present_flag equal to 0 specifies thatctu_lossless_flag is not present in the bitstream. Ifsps_ctu_lossless_present_flag is not presents, it is inferred to be 0.

FIG. 6 illustrates an exemplary Table 2 showing exemplary SPS syntax forsyntax element sps_ctu_lossless_present_flag, according to someembodiments of the present disclosure. Table 2 shows an exemplary SPSsyntax table when sps_ctu_lossless_present_flag is signaled in the SPS(emphases shown in box 601 and in italics). In the disclosed method,syntax element sps_transform_skip_enabled_flag is signaled only whensyntax element sps_ctu_lossless_present_flag is equal to 0. FIG. 7illustrates an exemplary Table 3 showing exemplary CTU syntax table whensyntax element sps_ctu_lossless_present_flag is signaled, according tosome embodiments of the present disclosure. Table 3 shows thecoding_tree_unit syntax table where the syntax element ctu_lossless_flagis conditionally signaled if SPS level syntax elementsps_ctu_lossless_present_flag is 1 (emphases shown in box 701 and initalics).

According to some embodiments, a slice level lossless flag can be usedto signal whether lossless coding is applied, Specifically, the losslessflag is signaled in the slice header. The following are the semantics ofthe disclosed slice level lossless flag, consistent with the presentembodiments:

slice_lossless_flag equal to 1 specifies that all of the CTUs of theslice are coded as lossless mode. slice_lossless_flag equal to 0specifies that the CTU level lossless flag of the slices are signaled.

If slice_lossless_flag is equal to 1, the lossy coding tools such asde-blocking filter, adaptive loop filter, sample adaptive offset, Lumamapping with chroma scaling (LMCS) are disabled, as follows:

-   -   Disable de-blocking: If slice_lossless_flag is equal to 1,        slice_deblocking_filter_disabled_flag is inferred to be 1.    -   Disable SAO and ALF: If slice_lossless_flag is equal to 1,        slice_sao_luma_flag, slice_sao_chroma_flag,        slice_alf_enabled_flag are inferred to be 0.    -   Disable LMCS and other coding tools: If slice_lossless_flag is        equal to 1, the CTU level lossless flags ctu_lossless_flag of        all of the CTUs of the slice are inferred to be 1 and LMCS        (since there is no slice level control flag to disable LMCS) and        other required coding tools are disabled at CTU level.

FIG. 8 illustrates an exemplary Table 4 showing exemplary slice_headersyntax of slice level lossless flag (emphases shown in boxes 801-803 andin italics), according to some embodiments of the present disclosure.FIG. 9 illustrates an exemplary Table 5 showing exemplarycoding_tree_unit syntax of slice level lossless coding (emphases shownin box 901 and in italics), according to some embodiments of the presentdisclosure. In Table 5, it is shown that the CTU level lossless flag isconditionally signaled if syntax element slice_lossless_flag is equal to0. If the syntax element slice_lossless_flag is equal to 1, the CTUlevel lossless flags ctu_lossless_flag is inferred to be 1.

According to some embodiments, a picture header can be used to signalwhether lossless coding is applied. Specifically, the lossless flag issignaled in the picture header (PH). The following are the semantics ofthe disclosed picture level lossless flag, consistent with the presentembodiments:

pic_lossless_flag equal to 1 specifies that all of the slices associatedwith the PH are coded as lossless mode. If pic_lossless_flag equal to 1,the slice level lossless flags slice_lossless_flag of all of the slicesassociated with the PH are inferred to be 1. pic_lossless_flag equal to0 specifies slice_lossless_flag may be present in the bit-stream.

If pic_lossless_flag is equal to 1, the following applies:

-   -   Disable de-blocking: If pic_lossless_flag is equal to 1,        pic_deblocking_filter_disabled_flag is inferred to be 1.    -   Disable SAO: If pic_lossless_flag is equal to 1,        pic_sao_enabled_present_flag, pic_sao_luma_enabled_flag,        pic_sao_chroma_enabled_flag are inferred to be 0.    -   Disable ALF: If pic_lossless_flag is equal to 1,        pic_alf_enabled_present_flag and pic_alf_enabled_flag are        inferred to be 0.    -   Disable LMCS: If pic_lossless_flag is equal to 1,        pic_lmcs_enabled_flag and pic_chroma_residual_scale_flag are        inferred to be 0.    -   Disable other coding tools: If pic_lossless_flag is equal to 1,        the slice level flags of all of the slices associated with the        PH are inferred to be 1. In addition, all of the CTU level        lossless flags are also inferred to be 1. The other necessary        coding tools are disabled at CTU level.

FIG. 10 illustrates an exemplary Table 6 showing exemplary pictureheader syntax table of picture level lossless coding (emphases shown inboxes 1001-1004 and in italics), according to some embodiments of thepresent disclosure. FIG. 11 illustrates an exemplary Table 7 showingexemplary slice header syntax table of picture level lossless codingwhen pic_lossless_flag is signaled (emphases shown in box 1101 and initalics), according to some embodiments of the present disclosure.

According to some embodiments, picture parameter set can be used tosignal whether lossless coding is applied. Specifically, the losslessflag can be signaled in picture parameter sets (PPS). The following arethe semantics of the disclosed PPS level lossless flag, consistent withthe present embodiments:

pps_lossless_flag equal to 1 specifies that all of the slices referringto the PPS is coded as lossless mode. If pps_lossless_flag is equal to1, the pps_deblocking_filter_disabled_flag is inferred to be 1.pps_lossless_flag equal to 0 specifies that the slices referring to thePPS is not coded as lossless mode.

If syntax element pps_lossless_flag is equal to 1, both the picturelevel lossless flags pic_lossless_flag and the slice level losslessflags slice_lossless_flag of all of the slices referred to that PPS areinferred to be 1. The CTU level lossless flags associated with that PPSare also inferred to be 1. Therefore, other coding tools may be disabledat CTU level.

FIG. 12 illustrates an exemplary Table 8 showing exemplary PPS syntaxtable with pps_lossless_flag of PPS level lossless coding (emphasesshown in box 1201 and in italics), according to some embodiments of thepresent disclosure. FIG. 13 illustrates an exemplary Table 9 showingexemplary picture header syntax table of PPS level lossless coding whenpps_lossless_flag is signaled (emphases shown in boxes 1301-4304 and initalics), according to some embodiments of the present disclosure.

According to some embodiments, the lossless flag is signaled in sequenceparameter sets (SPS). The following are the semantics of the disclosedSPS level lossless flag, consistent with the present embodiments:

sps_lossless_flag is equal to 1 specifies that the entire sequence iscoding as lossless mode. sps_lossless_flag is equal to 0 specifies thatthe entire sequence is not coding as lossless mode. If sps_lossless_flagis equal to 1, the following SPS flags are not signaled and inferred tobe as follows: — Disable LMCS: sps_lmcs_enabled_flag is inferred to be 0— Disable LFNST: sps_lfnst_enabled_flag is inferred to be 0 — Settransform size = 32: sps_max_luma_transform_size_64_flag is inferred tobe 0 — Disable joint Cb-Cr mode: sps_joint_cbcr_enabled_flag is inferredto be 0 — Disable SAO: sps_sao_enabled_flag is inferred to be 0 —Disable ALF: sps_alf_enabled_flag is inferred to be 0 — Allow transformskip: sps_transform_skip_enabled_flag is inferred to be 1 — Disable MTS:sps_mts_enabled_flag is inferred to be 0 — Disable SBT:sps_sbt_enabled_flag is inferred to be 0 — Disable LFNST:sps_ltnst_enabled_flag is inferred to be 0 — Disable ISP:sps_isp_enabled_flag is inferred to be 0

FIG. 14 illustrates an exemplary Table 10 showing exemplary SPS syntaxtable for sequence level lossless coding (emphases shown in box1401-1408 and in italics), according to some embodiments of the presentdisclosure. VVC 7 supports two residual coding methods: (a) regularresidual coding (RRC) (b) transform skip residual coding (TSRC). In VVC7 lossless coding, all of the coding blocks select TSRC. However, theRRC may achieve more coding gain as compared to TSRC especially in caseof camera capture contents, e.g., when lossless coding is used on thecurrent CTU. To maximize the coding gain, in some embodiments, anotherCTU level flag is used to signal the residual coding method of a CTU.The CTU level residual coding flag may be signaled if (and only if) thesyntax element ctu_lossless_flag is 1. Following are the semantics ofthe disclosed CTU residual coding flag, consistent with the presentembodiments:

ctu_rrc_flag[ xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] equal to 1specifies that all of the transform blocks of the coding tree unit atluma location ( xCtb, yCtb ) select regular residual coding method.ctu_rrc_flag[ xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] equal to 0specifies that the transform blocks of the coding tree unit at lumalocation ( xCtb, yCtb ) select residual coding method based on the valueof transform_skip_flag. If transform_skip_flag is equal 1, the transformblock selects TSRC. If transform_skip_flag is equal to 0, the transformblock selects RRC. When ctu_lossless_flag [ xCtb >> CtbLog2SizeY ][yCtb >> CtbLog2SizeY ] is 0, ctu_rrc_flag [ xCtb >> CtbLog2SizeY ][yCtb >> CtbLog2SizeY ] is inferred to be equal to 0. When ctu_rrc_flag [xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] is not present, it isinferred to be equal to 0.

FIG. 15 illustrates an exemplary Table 11 showing exemplarycoding_free_unit syntax table of CTU level residual coding flag(emphases shown in box 1501 and in italics), according to someembodiments of the present disclosure. FIG. 16 illustrates an exemplaryTable 12 showing exemplary transform_unit syntax of CTU level residualcoding flag (emphases shown in boxes 1601-1603 and in italics),according to some embodiments of the present disclosure.

In some embodiments, both syntax elements ctu_lossless_flag andctu_rrc_flag may be by-pass coded. In some embodiments, one of or bothof syntax elements ctu_lossless_flag and ctu_rrc_flag may be contextcoded.

The present disclosure also provides methods for configuring theinteraction between the lossless coding and various other coding tools.The details are described as follows.

According to some embodiments, if a CTU is coded as lossless mode,de-blocking filtering process of that CTU is skipped. According to someembodiments, the deblocking filter process is applied to all codingsubblock edges and transform block edges of a picture, except for sometypes of edges. FIG. 17 illustrates exemplary types of edges to whichdeblocking filter process is not applied (the portions in box 1701 andin italics show the changes of the disclosed methods as compred to VVC7draft), according to some embodiments of the present disclosure.

According to some embodiments, sample adaptive offset (SAO) is disabledfor a CTU if lossless coding is used. SAO is the process of addingoffset to de-blocked pixel values according to SAO type—e.g., based onedge direction/shape (Edge Offset) and pixel level (Band Offset) orunchanged (OFF). The SAO process is not mathematically lossless.Therefore, for lossless CTU, it is proposed to disable SAO. If thesyntax element ctu_lossless_flag is equal to 1, all of the SAO relatedsyntaxes of that CTU (such as syntax elements sao_merge_left_flag,sao_merge_up_flag, sao_type_idx_luma, sao_type_idx_chroma) are inferredto be 0. FIG. 18 illustrates an exemplary Table 13 showing exemplarycoding_tree_unit syntax table to disable SAO (emphases shown in box 1801and in italics), according to some embodiments of the presentdisclosure.

According to some embodiments, an adaptive loop filter (ALF) process isdisabled for a CTU if lossless coding is used. In VVC, an ALF withblock-based filter adaption is applied. Similar to de-blocking and SAO,ALF process is not mathematically lossless. Therefore, in order toachieve lossless coding of a CTU, it is proposed to disable ALF. FIG. 19illustrates an exemplary Table 14 showing exemplary coding tree unitsyntax to disable ALF (emphases shown in boxes 1901-1902 and initalics), according to some embodiments of the present disclosure. Ifsyntax element ctu_lossless_flag of a CTU is equal to 1, syntax elementalf_ctb_flag of all color components of that CTU are inferred to bezeros.

According to some embodiments, luma mapping with chroma scaling (LMCS)is disabled for a CTU if lossless coding is used. In VVC, a coding toolcalled the luma mapping with chroma scaling (LMCS) is added as a newprocessing block before the loop filters. LMCS has two maincomponents: 1) in-loop mapping of the luma component based on adaptivepiecewise linear models; 2) for the chroma components, luma-dependentchroma residual scaling is applied.

In some embodiments, if a CTU is coded as lossless mode, mapping of lumaand chroma residual scaling are disabled.

FIG. 20 illustrates an exemplary derivation of variable invLumaSample(emphases in box 2001 and in italics), according to some embodiments ofthe present disclosure.

Similarly, luma dependent chroma residual scaling process for chromasamples is disabled for lossless CTU. FIG. 21 illustrate exemplaryconditions to enable/disable chroma residual scaling (emphases in box2101 and in italics), according to some embodiments of the presentdisclosure.

According to some embodiments, sub block transform (SBT) is disabled fora CTU if lossless coding is used. In VVC, SBT is introduced for aninter-predicted CU. In this transform mode, only a sub-part of theresidual block is coded for the CU. When inter-predicted CU with cu_cbfequal to 1, cu_sbt_flag may be signaled to indicate whether the wholeresidual block or a sub-part of the residual block is coded. In theproposed method, if the coding tree unit lossless flag ctu_lossless_flagis equal to 1, SBT is not allowed for a coding unit belongs to that CTU.FIG. 22 illustrates an exemplary Table 15 showing exemplary coding unitsyntax of a method to disable SBT for lossless CTU (emphases shown inbox 2201 and in italics), according to some embodiments of the presentdisclosure.

According to some embodiments, signaling of Multiple Transform Selection(MTS) index is disabled for a CTU if lossless coding is used. In VVC7,in addition to DCT-II, an MTS scheme is used for residual coding bothinter and intra coded blocks. It uses multiple selected transforms fromthe DCT8/DST7. In some embodiments, signaling of the MIS index isdisabled if the current CTU is a lossless CTU, because such signaling isredundant as no transform is needed in the case of lossless CTU. FIG. 23illustrates an exemplary Table 16 showing exemplary coding unit syntaxto disable MTS of the lossless CTU, according to some embodiments of thepresent disclosure. Table 16 shows the related changes in the codingunit syntax table (emphases shown in box 2301 and in italics).

According to some embodiments, signaling of low-frequency non-separabletransform (LFNST) index is disabled for a CTU if lossless coding isused. In VVC, LFNST, which is known as reduced secondary transform, isapplied between forward primary transform and quantization (at encoder)and between de-quantization and inverse primary transform (at decoderside). In some embodiments, similar to MTS, signaling of LFNST index isalso disabled for a lossless CTU. FIG. 24 illustrates an exemplary Table17 showing exemplary coding unit syntax to disable LFNST for a losslessCTU (emphases shown in box 2401 and in italics), according to someembodiments of the present disclosure.

According to some embodiments, joint Cb-Cr mode is disabled for a CTU iflossless coding is used. In VVC, joint Cb-Cr mode is not mathematicallylossless. Therefore, it is proposed to disable joint Cb-Cr mode for alossless CTU. FIG. 25 illustrates an exemplary Table 18 showingexemplary part of transform unit syntax table to disable joint_cr_crmode (emphases shown in box 2501 and in italics), according to someembodiments of the present disclosure.

According to some embodiments. Intra Subpartition (ISP) mode is disabledfor a CTU if lossless coding is used. FIG. 26 illustrates an exemplaryTable 19 showing exemplary coding unit syntax table to disable ISP modefor a lossless CTU (emphases shown in box 2601 and in italics),according to some embodiments of the present disclosure.

According to some embodiments, a lossless CTU always select transformskip mode. Accordingly, if a CTU is lossless coded, transform_skip_flagof that CTU is not signaled and interred to be 1. FIG. 27 illustrates anexemplary Table 20 showing exemplary transform unit syntax oftransform_skip_flag signaling, according to some embodiments of thepresent disclosure. Table 20 shows the transform unit syntax of a methodwhere transform_skip_flag is signaled if ctu_lossless_flag is equal to 0(emphases shown in boxes 2701-2706 and in italics).

FIG. 28 illustrates a flowchart of an exemplary video processing method2800, according to some embodiments of the present disclosure. In someembodiments, method 2800, can be performed by an encoder (e.g., byprocess 200A of FIG. 2A or 200B of FIG. 2B), a decoder (e.g., by process300A of FIG. 3A or 300B of FIG. 3B) or performed by one or more softwareor hardware components of an apparatus (e.g., apparatus 400 of FIG. 4).For example, a processor (e.g., processor 402 of FIG. 4) can performmethod 2800. In some embodiments, method 2800 can be implemented by acomputer program product, embodied in a computer-readable medium,including computer-executable instructions, such as program code,executed by computers (e.g., apparatus 400 of FIG. 4).

At step 2801, a bitstream including a plurality of coding tree unit(CTUs) in a picture can be received. For example, video bitstream 228 ofFIG. 2A, FIG. 2B, FIG. 3A, FIG. 3B can be received.

At step 2803, a determination can be made on whether lossless coding isapplied to the plurality of CTUs, based on a plurality of flags,respectively. The plurality of flags can include a first flag associatedwith a first CTU. In some embodiments, each of the plurality of flagscan be a CTU level lossless flag, e.g., ctu_lossless_flag as shown inTable 1 of FIG. 5. In some embodiments, the first flag can be a slicelevel lossless flag (e.g., slice_lossless_flag as shown in Table 4 ofFIG. 8), a picture level lossless flag (e.g., pic_lossless_flag as shownin Table 6 of FIG. 10), a PPS level lossless flag (e.g.,pps_lossless_flag as shown in Table 8 of FIG. 12), or a SPS levellossless flag (e.g., sps_lossless_flag as shown in Table 10 of FIG. 14).

At step 2805, in response to a determination that lossless coding isapplied to the first CTU, lossless coding to the first CTU can beperformed. In some embodiments, method 2800 can include in response tothe first flag being not signaled in the bitstream, determining thatlossy coding is applied to the first CTU.

In some embodiments, method 2800 can include in response to thedetermination that lossless coding is applied to the first CTU,determining a residual coding method applied to transform blocks of thefirst CTU, based on a second flag (e.g., ctu_rrc_flag as shown in Table11 of FIG. 15, Table 12 of FIG. 16, Table 13 of FIG. 18, or Table 14 ofFIG. 19). In response to the second flag having a first value (e.g., 1),method 2800 can determine that a first residual coding method (e.g.,regular residual coding method) is applied to the transform blocks. Inresponse to the second flag having a second value (e.g., 0), method 2800can determine a residual coding method applied to the transform blocks,based on a third flag (e.g., transform_skip_flag). In response to thethird flag having a third value (e.g., 0), method 2800 can determinethat the first residual coding method (e.g., regular residual codingmethod) is applied to the transform blocks. In response to the thirdflag having a fourth value (e.g., 1), determining that a second residualcoding method (e.g., transform skip residual coding method) is appliedto the transform blocks.

In some embodiments, method 2800 can include in response to thedetermination that lossless coding is applied to the first CTU, codingthe first CTU in a transform skip mode regardless of whether atransform-skip flag for the first CTU is signaled in the bitstream.

In some embodiments, method 2800 can include determining whether thefirst flag (e.g., ctu_lossless_flag as shown in Table 1 of FIG. 5) issignaled in the bitstream based on a fourth flag. The fourth flag is aSPS level flag (e.g., sps_ctu_lossless_present_flag as shown in Table 2of FIG. 6). In response to the fourth flag being not signaled in thebitstream, method 2800 can determine that the bitstream does not includethe first flag.

In some embodiments, method 2800 can include: in response to a fifthflag having a fifth value, determining that lossless coding is appliedto a picture slice including the first CTU, or in response to the fifthflag having a sixth value, determining that the first flag is signaledin the bitstream. The fifth flag can be a slice level lossless flag(e.g., slice lossless flag as shown in Table 4 of FIG. 8 and Table 5 ofFIG. 9).

In some embodiments, method 2800 can include: in response to a sixthflag having a seventh value, determining that lossless coding is appliedto a picture including the first CTU, or in response to the sixth flaghaving an eighth value, determining that the fifth flag is signaled inthe bitstream. The sixth flag can be a picture level lossless flag(e.g., pic_lossless_flag as shown in Table 6 of FIG. 10 and Table 7 ofFIG. 11).

In some embodiments, method 2800 can include: in response to a seventhflag having a ninth value, determining that lossless coding is appliedto a picture associated with a PPS and including the first CTU, or inresponse to the seventh flag having a tenth value, determining that thesixth flag is signaled in the bitstream. The seventh flag can be a PPSlevel lossless flag (e.g., pps_lossless_flag as shown in Table 8 of FIG.12 and Table 9 of FIG. 13).

In some embodiments, method 2800 can include: in response to an eighthflag having an eleventh value, determining that lossless coding isapplied to a picture associated with a SPS and including the first CTU,or in response to the eighth flag having a twelfth value, determiningthat lossy coding is applied to one or more first CTUs associated withthe SPS. The eighth flag can be a SPS level lossless flag (e.g.,sps_lossless_flag as shown in Table 10 of FIG. 14). In some embodiment,in response to the eighth flag having a twelfth value, CTU levellossless flag, a slice level lossless flag, a picture level losslessflag, or a PPS level lossless flag can be signaled to indicate whether afirst CTU, a slice, or a picture can be coded with a lossy coding mode.

In some embodiments, method 2800 can include in response to thedetermination that lossless coding is applied to the first CTU,disabling, for the first CTU, one or more of: a de-clocking filteringprocess; an SAO process; an ALF process; LMCS; lama dependent chromaresidual scaling process; SBT; signaling of MTS index; signaling ofLFNST index; a joint Cb-Cr mode; or an ISP mode.

To achieve mixed coding, in which one part of an image is lossless codedand another part of the image is lossy coded, LMCS needs to be disabledfor a whole picture even including the lossy part of the picture,because the current VVC design does not provide a way to control theLMCS locally. The present disclosure also provides embodiments forcontrolling the LMCS locally.

In some embodiments, a CTB level LMCS flag can be signaled to controlLMCS in the CTB level. The semantics of the proposed CTB level flag aregiven below.

“lmcs_ctb_luma_flag, [xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]” equal to1 specifies that the luma mapping with chroma scaling is applied to theluma coding tree block at luma location (xCtb, yCtb).

“lmes_ctb_luma_flag[cIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]” equalto 0 specifies that the luma mapping with chroma scaling is not appliedto the luma coding tree block the coding tree block at luma location(xCtb, yCtb).

When

-   “lmcs_ctb_luma_flag[cIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]”    is not present, it is inferred to be equal to 0.

“lmcs_ctb_chroma_residual_scale_flag[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]”equal to 1 specifies that chroma residual scaling is applied to thechroma coding tree block at Hanna location (xCtb, yCtb).

“lmcs_ctb_chroma_residual_scale_flag[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]” equal to 0 specifies that thechroma residual scaling is not applied to the chroma coding tree blockthe coding tree block at luma location xCtb, yCtb).

When

-   “lmcs_ctb_chroma_residual_scale_flag[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]”    is not present, it is inferred to be equal to 0.

FIG. 29 illustrates an exemplary Table 21 showing exemplary syntax forcontrolling luma mapping with chroma scaling (LMCS) at the CTB level,according to some embodiments of the present disclosure. Emphases of thesyntax are shown in box 2901 and in italics.

In picture reconstruction with mapping process for luma samples, inputto this process includes the following: current picture; a variablenCurrSw specifying the block width; a variable nCurrSh specifying theblock height; an (nCurrSw)×(nCurrSh) array predSamples specifying theluma predicted samples of the current block; and an (nCurrSw)×(nCurrSh)array resSamples specifying the luma residual samples of the currentblock. Moreover, consistent with the disclosed embodiment, the input tothe process also includes the following requirement:lmcs_ctb_luma_flag[xCurr>>CtbLog2SizeY][yCurr>>CtbLog2SizeY] of the lumacoding tree block.

Outputs of this process is a reconstructed luma picture sample arrayrecSamples:

-   -   If lmcs_ctb_luma_flag[xCurr>>CtbLog2SizeY][yCurr>>CtbLog2SizeY]        is equal to 0, the (nCurrSw)×(nCurrSh) block of the        reconstructed samples recSamples at location (xCurr, yCurr) is        derived as follows for i=0 . . . nCurrSw−1, j=0 . . . nCurrSh−1:        recSamples[xCurr+i][yCurr+j]=Clip1(predSamples[i][j]+resSamples[i][j])

-   Otherwise, the (nCurrSw)×(nCurrSh) array of mapped predicted luma    samples predMapSamples is derived as follows:    -   If one of the following conditions is true, predMapSamples[i][j]        is set equal to predSamples[i][j] for i=0 . . . nCurrSw−1, j=0 .        . . nCurrSh−1:        -   CuPredMode[0][xCurr][yCurr] is equal to MODE_INTRA.        -   CuPredMode[0][xCurr][yCurr] is equal to MODE_IBC.        -   CuPredMode[0][xCurr][yCurr] is equal to MODE_PLT.        -   CuPredMode[0][xCurr][yCurr] is equal to MODE_INTER and            ciip_flag[xCurr][yCurr] is equal to 1.    -   Otherwise (CuPredMode[0][xCurr][yCurr] is equal to MODE_INTER        and ciip_flag[xCurr][yCurr] is equal to 0), the following        applies:        idxY=predSamples[i][j]>>Log 2(OrgCW)        predMapSamples[i][j]=LmcsPivot[idxY]+ScaleCoeff[idxY]*(predSamples[i][j]−InputPivot[idxY])+(1<<10))>>11

with i=0 . . . nCurrSw−1, j=0 . . . nCurrSh−1

The reconstructed luma picture sample recSamples is derived as follows:recSamples[xCurr+i][yCurr+j]=Clip1(predMapSamples[i][j]+resSamples[i][j]]

with i=0 . . . nCurrSw−1, j=0 . . . nCurrSh−1

In picture reconstruction with luma dependent chroma residual scalingprocess for chroma samples, input to this process includes thefollowing: a chroma location (xCurr, yCurr) of the top-left chromasample of the current chroma transform block relative to the top-leftchroma sample of the current picture; a variable nCurrSw specifying thechroma transform block width; a variable nCurrSh specifying the chromatransform block height; a variable tuCbfChroma specifying the codedblock flag of the current chroma transform block; an (nCurrSw)×(nCurrSh)array predSamples specifying the chroma prediction samples of thecurrent block; an (nCurrSw)×(nCurrSh) array resSamples specifying thechroma residual samples of the current block; a location (xCtb, yCtb)specifying the top-left luma sample of the current coding tree unitrelative to the top left sample of the current picture component;

-   lmcs_ctb_chroma_residual_scale_flag    [xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] of the coding tree block.

Output of this process is a reconstructed chroma picture sample arrayrecSamples.

The variable sizeY is set equal to Min(CtbSizeY, 64).

The reconstructed chroma picture sample recSamples is derived as followsfor i=0 . . . nCurrSw−1, j=0 . . . nCurrSh−1.

-   If one of the following conditions is true, recSamples[i][yCurr+j]    is set equal to Clip1(predSamples[i][j]+resSamples[i][j]):    -   pic_chroma_residual_scale_flag is equal to 0.    -   nCurrSw*nCurrSh is less than or equal to 4.    -   tu_cbf_cb [xCurr][yCurr] is equal to 0 and tu_cbf_cr        [xCurr][yCurr] is equal to 0.    -   lmcs_ctb_chroma_residual_scale_flag        [xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is equal to 0-   Otherwise, the following applies:    -   The current luma location (xCurrY, yCurrY) is derived as        follows:        (xCurrY,yCurrY)=(xCurr*SubWidthC,yCurr*SubHeightC)

The luma location (xCuCb, yCuCb) is specified as the)p-left luma samplelocation of the coding unit that contains the luma sample at(xCurrY/sizeY*sizeY, yCurrY/sizeY*sizeY).

-   The variables availL and availT are derived as follows:    -   The derivation process for neighbouring block availability as        specified in clause 6.4.4 is invoked with the location (xCurr,        yCurr) set equal to (xCuCb, yCuCb), the neighbouring luma        location (xNbY, yNbY) set equal to (xCuCb−1, yCuCb),        checkPredModeY set equal to FALSE, and cIdx set equal to 0 as        inputs, and the output is assigned to availL.    -   The derivation process for neighbouring block availability as        specified in clause 6.4.4 is invoked with the location (xCurr,        yCurr) set equal to (xCuCb, yCuCb), the neighbouring luma        location (xNbY, yNbY) set equal to (xCuCb, yCuCb−1),        checkPredModeY set equal to FALSE, and cIdx set equal to 0 as        inputs, and the output is assigned to availT.-   The variable currPic specifies the array of reconstructed luma    samples in the current picture.-   For the derivation of the variable varScale the following ordered    steps apply:

1. The variable invAvgLuma is derived as follows:

-   -   The array recLuma[i] with i=0 . . . (2*sizeY−1) and the variable        cnt are derived as follows:        -   The variable cnt is set equal to 0.        -   When availL is equal to TRUE, the array recLuma[i] with i=0            . . . sizeY−1 is set equal to            -   currPic[xCuCb−1][Min(yCuCb+i,                pic_height_in_luma_samples−1)] with i=0 . . . sizeY−1,                and cnt is set equal to sizeY,        -   When availT is equal to TRUE, the array recLuma[cnt+i] with            i=0 . . . sizeY−1 is set equal to currPic[Min(xCuCb+i,            pic_width_in_luma_samples−1)][yCuCb−1] with i=0 . . .            sizeY−1, and cnt is set equal to (cnt+sizeY).        -   The variable invAvgLuma is derived as follows:            -   if cnt is greater than 0, the following applies:                invAvgLuma=Clip1((Σ_(k=0)                ^(cnt−1)recLuma[k]+(cnt>>1))>>Log 2(cnt))                Otherwise (cnt is equal to 0), the following applies:                invAvgLuma=1<<(BitDepth−1)

2. The variable idxYInv is derived by invoking the identification ofpiece-wise function index process for a luma sample as specified inclause 8.8.2.3 with the variable lumaSample set equal to invAvgLuma asthe input and idxYInv as the output.

3. The variable varScale is derived as follows:varScale=ChromaScaleCoeff[idxYInv]

-   The reconstructed chroma picture sample array recSamples is derived    as follows:    -   If tuCbfChroma is equal to 1, the following applies:        resSamples[i][j]=Clip3(−(1<<BitDepth),(1<<BitDepth)−1,resSamples[i][j])        recSamples[xCurr+i][yCurr+j]=Clip1(predSamples[i][j]+Sign(resSamples[i][j])*((Abs(resSamples[i][j])*varScale+(1<<10))>>11))

Otherwise (tuCbfChroma is equal to 0), the following applies:recSamples[xCurr+i][yCurr+j]=Clip1(predSamples[i][j])

In inverse mapping process for a luma sample, input to this process isas below:

-   -   a luma sample lumaSample.    -   a location (xCtb, yCtb) specifying the top-left luma sample of        the current coding tree unit relative to the top left sample of        the current picture component,    -   lmes_ctb_luma_flag[0][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] of        the coding tree unit

Output of this process is a modified luma sample invLumaSample

The value of invLumaSample is derived as follows:

-   If pic_lmcs_enabled_flag of the slice that contains the luma sample    lumaSample is equal to 1, and    lmcs_ctb_luma_flag[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is not    equal to zero the following ordered steps apply:-   The variable idxYInv is derived by invoking the identification of    piece-wise function index process for a luma sample as specified in    clause 8.8.2.3 with lumaSample as the input and idxYInv as the    output.

The variable invSample is derived as follows:invSample=InputPivot[idxYInv]+(InvScaleCoeff[idxYInv]*(lumaSample−LmcsPivot[idxYInv])+(1<<10))>>11

The inverse mapped luma sample invLumaSample is derived as follows:invLumaSample=Clip1(invSample)

Otherwise, invLumaSample is set equal to lumaSample

In some embodiments, the proposed LMCS control flags are signaled atslice header. A flag called slice_lmcs_lima_enabled_flag is signaled ineach slice header to control whether LMCS is enabled for that slice ornot. FIG. 30 illustrates an exemplary Table 22 showing exemplary sliceheader syntax for signaling LMCS control flags at slice level, accordingto some embodiments of the present disclosure.

“slice_lmes_luma_enabled_flag” equal to 1 specifies that luma mappingwith chroma scaling is enabled for the luma component of the slices.

-   “slice_lmcs_luma_enabled_flag” equal to 0 specifies that luma    mapping with chroma scaling is not applied to the luma component of    the slice. When “pic_lmcs_enabled_flag” is not present, its value is    inferred to be equal to 0.

“slice_chroma_residual_scale_flag” equal to 1 specifies that chromaresidual scaling is enabled for the slices.“slice_chroma_residual_scale_flag” equal to 0 specifies that chromaresidual scaling is disabled for the slice.

In some embodiments, the proposed slice level LMCS control flags aresignaled at slice header to control LMCS for both luma and chroma. Forinstance, slice_chroma_residual_scale_flag being equal to 1 indicatethat LMCS is enable for both luma and chroma. Ifslice_chroma_residual_scale_flag is equal to 0, LMCS is disabled forboth luma and chroma of that slice.

The embodiments of the present disclosure may further be described usingthe following clauses:

1. A video processing method, comprising:

receiving a bitstream comprising a plurality of coding tree unit (CTUs)in a picture;

determining whether lossless coding is applied to the plurality of CTUs,based on a plurality of flags, respectively,

wherein the plurality of flags comprise a first flag associated with afirst CTU, and the method further comprises:

in response to a determination that lossless coding is applied to thefirst CTU, performing lossless coding to the first CTU.

2. The method of clause 1, wherein each of the plurality of flags is aCTU level lossless flag.

3. The method of any one of clauses 1 and 2, further comprising:

in response to the first flag being not signaled in the bitstream,determining that lossy coding is applied to the first CTU.

4. The method of any one of clauses 1-3, further comprising:

in response to the determination that lossless coding is applied to thefirst CTU, determining, based on a second flag, a residual coding methodapplied to transform blocks of the first CTU.

5. The method of clause 4, further comprising:

in response to the second flag having a first value, determining that afirst residual coding method is applied to the transform blocks.

6. The method of clause 4, further comprising:

in response to the second flag having a second value, determining avalue of a third flag, and

in response to the third flag having a third value, determining that afirst residual coding method is applied to the transform blocks, or

in response to the third flag having a fourth value, determining that asecond residual coding method is applied to the transform blocks.

7. The method of any one of clauses 1-6, further comprising:

in response to the determination that lossless coding is applied to thefirst CTU, coding the first CTU in a transform skip mode regardless ofwhether a transform-skip flag for the first CTU is signaled in thebitstream.

8. The method of any one of clauses 1-7, further comprising:

determining, based on a fourth flag, whether the first flag is signaledin the bitstream, the fourth flag being a sequence parameter sets (SPS)level flag.

9. The method of clause 8, further comprising:

in response to the fourth flag being not signaled in the bitstream,determining that the bitstream does not comprise the first flag.

10. The method of any one of clauses 1-9, further comprising:

in response to a fifth flag having a fifth value, determining thatlossless coding is applied to a picture slice including the first CTU;or

in response to the fifth flag having a sixth value, determining that thefirst flag is signaled in the bitstream,

wherein the fifth flag is a slice level lossless flag.

11. The method of clause 10, further comprising:

in response to a sixth flag having a seventh value, determining thatlossless coding is applied to a picture including the first CTU; or

in response to the sixth flag having an eighth value, determining thatthe fifth flag is signaled in the bitstream,

wherein the sixth flag is a picture level lossless flag.

12. The method of clause 11, further comprising:

in response to a seventh flag having a ninth value, determining thatlossless coding is applied to a picture associated with a pictureparameter sets (PPS) and including the first CTU; or

in response to the seventh flag having a tenth value, determining thatthe sixth flag is signaled in the bitstream,

wherein the seventh flag is a PPS level lossless flag.

13. The method of any of clauses 1-12, further comprising:

in response to an eighth flag having an eleventh value, determining thatlossless coding is applied to a picture associated with a SPS andincluding the first CTU; or

in response to the eighth flag having a twelfth value, determining thatlossy coding is applied to one or more CTUs associated with the SPS,

wherein the eighth flag is a SPS level lossless flag.

14. The method of clause 1, wherein the first flag is a slice levellossless flag, a picture level lossless flag, a PPS level lossless flag,or a SPS level lossless flag.

15. The method of any one of clauses 1-14, further comprising:

in response to the determination that lossless coding is applied to thefirst CTU, disabling, for the first CTU, one or more of:

a de-clocking filtering process;

a sample adaptive offset (SAO) process;

an adaptive loop filter (ALF) process;

luma mapping with chroma scaling (LMCS);

luma dependent chroma residual scaling process;

sub block transform (SBT);

signaling of Multiple Transform Selection (MTS) index;

signaling of low-frequency non-separable transform (LFNST) index;

a joint Cb-Cr mode; or

an Intra Subpartition (ISP) mode.

16. A video processing apparatus, comprising:

at least one memory for storing instructions; and

at least one processor configured to execute the instructions to causethe apparatus to perform:

-   -   receiving a bitstream comprising a plurality of coding tree unit        (CPUs) in a picture;    -   determining whether lossless coding is applied to the plurality        of CTUs, based on a plurality of flags, respectively,    -   wherein the plurality of flags comprise a first flag associated        with a first CTU, and the method further comprises:    -   in response to a determination that lossless coding is applied        to the first CTU, performing lossless coding to the first CTU.

17. The apparatus of clause 16, wherein each of the plurality of flagsis a CTU level lossless flag.

18. The apparatus of any one of clauses 16 and 17, wherein the at leastone processor is configured to execute the instructions to cause theapparatus to perform:

in response to the first flag being not signaled in the bitstream,determining that lossy coding is applied to the first CTU.

19. The apparatus of any one of clauses 16-18, wherein the at least oneprocessor is configured to execute the instructions to cause theapparatus to perform:

in response to the determination that lossless coding is applied to thefirst CTU, determining, based on a second flag, a residual coding methodapplied to transform blocks of the first CTU.

20. The apparatus of clause 19, wherein the at least one processor isconfigured to execute the instructions to cause the apparatus toperform:

in response to the second flag having a first value, determining that afirst residual coding method is applied to the transform blocks.

21. The apparatus of clause 19, wherein the at least one processor isconfigured to execute the instructions to cause the apparatus toperform:

in response to the second flag having a second value, determining avalue of a third flag; and

-   -   in response to the third flag having a third value, determining        that a first residual coding method is applied to the transform        blocks, or    -   in response to the third flag having a fourth value, determining        that a second residual coding method is applied to the transform        blocks.

22. The apparatus of any one of clauses 16-21, wherein the at least oneprocessor is configured to execute the instructions to cause theapparatus to perform: in response to the determination that losslesscoding is applied to the first CTU, coding the first CTU in a transformskip mode regardless of whether a transform-skip flag for the first CTUis signaled in the bitstream.

23. The apparatus of any one of clauses 16-22, wherein the at least oneprocessor is configured to execute the instructions to cause theapparatus to perform:

determining, based on a fourth flag, whether the first flag is signaledin the bitstream, the fourth flag being a sequence parameter sets (SPS)level flag.

24. The apparatus of clause 23, wherein the at least one processor isconfigured to execute the instructions to cause the apparatus toperform:

in response to the fourth flag being not signaled in the bitstream,determining that the bitstream does not comprise the first flag.

25. The apparatus of any one of clauses 16-24, wherein the at least oneprocessor is configured to execute the instructions to cause theapparatus to perform:

in response to a fifth flag having a fifth value, determining thatlossless coding is applied to a picture slice including the first CTU;or

in response to the fifth flag having a sixth value, determining that thefirst flag is signaled in the bitstream,

wherein the fifth flag is a slice level lossless flag.

26. The apparatus of clause 25, wherein the at least one processor isconfigured to execute the instructions to cause the apparatus toperform:

in response to a sixth flag having a seventh value, determining thatlossless coding is applied to a picture including the first CTU or

in response to the sixth flag having an eighth value, determining thatthe fifth flag is signaled in the bitstream,

wherein the sixth flag is a picture level lossless flag.

27. The apparatus of clause 26, wherein the at least one processor isconfigured to execute the instructions to cause the apparatus toperform:

in response to a seventh flag having a ninth value, determining thatlossless coding is applied to a picture associated with a pictureparameter sets (PPS) and including the first CTU; or

in response to the seventh flag having a tenth value, determining thatthe sixth flag is signaled in the bitstream,

wherein the seventh flag is a PPS level lossless flag.

28. The apparatus of any one of clauses 16-27, wherein the at least oneprocessor is configured to execute the instructions to cause theapparatus to perform:

in response to an eighth flag having an eleventh value, determining thatlossless coding is applied to a picture associated with a SPS andincluding the first CTU; or

in response to the eighth flag having a twelfth value, determining thatlossy coding is applied to one or more CTUs associated with the SPS,

-   -   wherein the eighth flag is a SPS level lossless flag.

29. The apparatus of clause 16, wherein the first flag is a slice levellossless flag, a picture level lossless flag, a PPS level lossless flag,or a SPS level lossless flag.

30. The apparatus of any one of clauses 16-29, wherein the at least oneprocessor is configured to execute the instructions to cause theapparatus to perform:

in response to the determination that lossless coding is applied to thefirst CTU, disabling, for the first CTU, one or more of:

a de-clocking filtering process;

a sample adaptive offset (SAO) process;

an adaptive loop filter (ALF) process;

luma mapping with chroma scaling (LMCS);

luma dependent chroma residual scaling process;

sub block transform (SBT);

signaling of Multiple Transform Selection (MTS) index;

signaling of low-frequency non-separable transform (LFNST) index;

a joint Cb-Cr mode; or

an Intra Subpartition (ISP) mode.

31. A non-transitory computer readable storage medium storing a set ofinstructions that are executable by one or more processing devices tocause a video processing apparatus to perform a method comprising:

receiving a bitstream comprising a plurality of coding tree unit (CTUs)in a picture;

determining whether lossless coding is applied to the plurality of CTUs,based on a plurality of flags, respectively,

wherein the plurality of flags comprise a first flag associated with afirst CTU, and the method further comprises:

in response to a determination that lossless coding is applied to thefirst CTU, performing lossless coding to the first CTU.

32. The non-transitory computer readable storage medium of clause 31,wherein each of the plurality of flags is a CTU level lossless flag.

33. The on-transitory computer readable storage medium of any one ofclauses 31 and 32, wherein the set of instructions are executable by theone or more processing devices to cause the video processing apparatusto perform:

in response to the first flag being not signaled in the bitstream,determining that lossy coding is applied to the first CTU.

34. The non-transitory computer readable storage medium of any one ofclauses 31-33, wherein the set of instructions are executable by the oneor more processing devices to cause the video processing apparatus toperform:

in response to the determination that lossless coding is applied to thefirst CTU, determining, based on a second flag, a residual coding methodapplied to transform blocks of the first CTU.

35. The non-transitory computer readable storage medium of clause 34,wherein the set of instructions are executable by the one or moreprocessing devices to cause the video processing apparatus to perform:

in response to the second flag having a first value, determining that afirst residual coding method is applied to the transform blocks.

36. The non-transitory computer readable storage medium of clause 34,wherein the set of instructions are executable by the one or moreprocessing devices to cause the video processing apparatus to perform:

in response to the second flag having a second value, determining avalue of a third flag; and

in response to the third flag having a third value, determining that afirst residual coding method is applied to the transform blocks, or

in response to the third flag having a fourth value, determining that asecond residual coding method is applied to the transform blocks.

37. The non-transitory computer readable storage medium of any one ofclauses 31-36, wherein the set of instructions are executable by the oneor more processing devices to cause the video processing apparatus toperform:

in response to the determination that lossless coding is applied to thefirst CTU, coding the first CTU in a transform skip mode regardless ofwhether a transform-skip flag for the first CTU is signaled in thebitstream.

38. The non-transitory computer readable storage medium of any one ofclauses 31-37, wherein the set of instructions are executable by the oneor more processing devices to cause the video processing apparatus toperform:

determining, based on a fourth flag, whether the first flag is signaledin the bitstream, the fourth flag being a sequence parameter sets (SPS)level flag.

39. The non-transitory computer readable storage medium of clause 38,wherein the set of instructions are executable by the one or moreprocessing devices to cause the video processing apparatus to perform:

in response to the fourth flag being not signaled in the bitstream,determining that the bitstream does not comprise the first flag.

40. The non-transitory computer readable storage medium of any one ofclauses 31-39, wherein the set of instructions are executable by the oneor more processing devices to cause the video processing apparatus toperform:

in response to a fifth flag having a fifth value, determining thatlossless coding is applied to a picture slice including the first CTU;or

in response to the fifth flag having a sixth value, determining that thefirst flag is signaled in the bitstream,

wherein the fifth flag is a slice level lossless flag.

41. The non-transitory computer readable storage medium of 40, whereinthe set of instructions are executable by the one or more processingdevices to cause the video processing apparatus to perform:

in response to a sixth flag having a seventh value, determining thatlossless coding is applied to a picture including the first CTU; or

in response to the sixth flag having an eighth value, determining thatthe fifth flag is signaled in the bitstream,

wherein the sixth flag is a picture level lossless flag.

42. The non-transitory computer readable storage medium of clause 41,wherein the set of instructions are executable by the one or moreprocessing devices to cause the video processing apparatus to perform:

in response to a seventh flag having a ninth value, determining thatlossless coding is applied to a picture associated with a pictureparameter sets (PPS) and including the first CTU; or

in response to the seventh flag having a tenth value, determining thatthe sixth flag is signaled in the bitstream,

wherein the seventh flag is a PPS level lossless flag.

43. The non-transitory computer readable storage medium of any one ofclauses 31-42, wherein the set of instructions are executable by the oneor more processing devices to cause the video processing apparatus toperform:

in response to an eighth flag having an eleventh value, determining thatlossless coding is applied to a picture associated with a SPS andincluding the first CTU; or

in response to the eighth flag having a twelfth value, determining thatlossy coding is applied to one or more CTUs associated with the SPS,

wherein the eighth flag is a SPS level lossless flag.

44. The non-transitory computer readable storage medium of clause 31,wherein the first flag is a slice level lossless flag, a picture levellossless flag, a PPS level lossless flag, or a SPS level lossless flag.

45. The non-transitory computer readable storage medium of any one ofclauses 31-44, wherein the set of instructions are executable by the oneor more processing devices to cause the video processing apparatus toperform:

in response to the determination that lossless coding is applied to thefirst CTU, disabling, for the first CTU, one or more of:

a de-clocking filtering process;

a sample adaptive offset (SAO) process;

an adaptive loop filter (ALF) process;

luma mapping with chroma scaling (LMCS);

luma dependent chroma residual scaling process;

sub block transform (SBT);

signaling of Multiple Transform Selection (MTS) index;

signaling of low-frequency non-separable transform (LFNST) index;

a joint Cb-Cr mode; or

an Intra Subpartition (ISP) mode.

46. A video processing method, comprising:

receiving a bitstream representing a picture sequence, the bitstreamincluding a parameter set for the picture sequence;

determining whether lama mapping with chroma scaling (LMCS) is enabledfor the picture sequence;

in response to the determination that LMCS is enabled for the picturesequence, determining if LMCS is enabled for a coding tree block (CTB)of the picture sequence.

47. The method of clause 46, further comprising:

in response to the determination that LMCS is enabled for the CTB of thepicture sequence, applying LMCS on the CTB.

In some embodiments, a non-transitory computer-readable storage mediumincluding instructions is also provided, and the instructions may beexecuted by a device (such as the disclosed encoder and decoder), forperforming the above-described methods. Common forms of non-transitorymedia include, for example, a floppy disk, a flexible disk, hard disk,solid state drive, magnetic tape, or any other magnetic data storagemedium, a CD-ROM, any other optical data storage medium, any physicalmedium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROMor any other flash memory, NVRAM, a cache, a register, any other memorychip or cartridge, and networked versions of the same. The device mayinclude one or more processors (CPUs), an input/output interface, anetwork interface, and/or a memory.

It should be noted that, the relational terms herein such as “first” and“second” are used only to differentiate an entity or operation fromanother entity or operation, and do not require or imply any actualrelationship or sequence between these entities or operations. Moreover,the words “comprising,” “having,” “containing,” and “including,” andother similar forms are intended to be equivalent in meaning and be openended in that an item or items following any one of these words is notmeant to be an exhaustive listing of such item or items, or meant to belimited to only the listed item or items.

As used herein, unless specifically stated otherwise, the term “or”encompasses all possible combinations, except where infeasible. Forexample, if it is stated that a database may include A or B, then,unless specifically stated otherwise or infeasible, the database mayinclude A, or B, or A and B. As a second example, if it is stated that adatabase may include A, B, or C, then, unless specifically statedotherwise or infeasible, the database may include A, or B, or C, or Aand B, or A and C, or B and C, or A and B and C.

It is appreciated that the above described embodiments can beimplemented by hardware, or software (program codes), or a combinationof hardware and software. If implemented by software, it may be storedin the above-described computer-readable media. The software, whenexecuted by the processor can perform the disclosed methods. Thecomputing units and other functional units described in this disclosurecan be implemented by hardware, or software, or a combination ofhardware and software. One of ordinary skill in the art will alsounderstand that multiple ones of the above described modules/units maybe combined as one module/unit, and each of the above describedmodules/units may be further divided into a plurality ofsub-modules/sub-units.

In the foregoing specification, embodiments have been described withreference to numerous specific details that can vary from implementationto implementation. Certain adaptations and modifications of thedescribed embodiments can be made. Other embodiments can be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims. It is also intended that the sequence of steps shown in figuresare only for illustrative purposes and are not intended to be limited toany particular sequence of steps. As such, those skilled in the art canappreciate that these steps can be performed in a different order whileimplementing the same method.

In the drawings and specification, there have been disclosed exemplaryembodiments. However, many variations and modifications can be made tothese embodiments. Accordingly, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

What is claimed is:
 1. A video processing method, comprising: receivinga bitstream comprising a plurality of coding tree unit (CTUs) in apicture; determining whether lossless coding is applied to the pluralityof CTUs, based on a plurality of flags, respectively, wherein theplurality of flags comprise a first flag associated with a first CTU andeach of the plurality of flags is a CTU level lossless flag, and themethod further comprises: in response to a determination that losslesscoding is applied to the first CTU, performing lossless coding to thefirst CTU.
 2. The method of claim 1, further comprising: in response tothe first flag being not signaled in the bitstream, determining thatlossy coding is applied to the first CTU.
 3. The method of claim 1,further comprising: in response to the determination that losslesscoding is applied to the first CTU, determining, based on a second flag,a residual coding method applied to transform blocks of the first CTU.4. The method of claim 3, further comprising: in response to the secondflag having a first value, determining that a first residual codingmethod is applied to the transform blocks.
 5. The method of claim 3,further comprising: in response to the second flag having a secondvalue, determining a value of a third flag; and in response to the thirdflag having a third value, determining that a first residual codingmethod is applied to the transform blocks, or in response to the thirdflag having a fourth value, determining that a second residual codingmethod is applied to the transform blocks.
 6. The method of claim 1,further comprising: in response to the determination that losslesscoding is applied to the first CTU, coding the first CTU in a transformskip mode regardless of whether a transform-skip flag for the first CTUis signaled in the bitstream.
 7. The method of claim 1, furthercomprising: determining, based on a fourth flag, whether the first flagis signaled in the bitstream, the fourth flag being a sequence parametersets (SPS) level flag.
 8. The method of claim 7, further comprising: inresponse to the fourth flag being not signaled in the bitstream,determining that the bitstream does not comprise the first flag.
 9. Themethod of claim 1, further comprising: in response to a fifth flaghaving a fifth value, determining that lossless coding is applied to apicture slice including the first CTU; or in response to the fifth flaghaving a sixth value, determining that the first flag is signaled in thebitstream, wherein the fifth flag is a slice level lossless flag. 10.The method of claim 9, further comprising: in response to a sixth flaghaving a seventh value, determining that lossless coding is applied to apicture including the first CTU; or in response to the sixth flag havingan eighth value, determining that the fifth flag is signaled in thebitstream, wherein the sixth flag is a picture level lossless flag. 11.The method of claim 10, further comprising: in response to a seventhflag having a ninth value, determining that lossless coding is appliedto a picture associated with a picture parameter sets (PPS) andincluding the first CTU; or in response to the seventh flag having atenth value, determining that the sixth flag is signaled in thebitstream, wherein the seventh flag is a PPS level lossless flag. 12.The method of claim 1, further comprising: in response to an eighth flaghaving an eleventh value, determining that lossless coding is applied toa picture associated with a SPS and including the first CTU; or inresponse to the eighth flag having a twelfth value, determining thatlossy coding is applied to one or more CTUs associated with the SPS,wherein the eighth flag is a SPS level lossless flag.
 13. The method ofclaim 1, further comprising: in response to the determination thatlossless coding is applied to the first CTU, disabling, for the firstCTU, one or more of: a de-blocking filtering process; a sample adaptiveoffset (SAO) process; an adaptive loop filter (ALF) process; lumamapping with chroma scaling (LMCS); luma dependent chroma residualscaling process; sub block transform (SBT); signaling of MultipleTransform Selection (MTS) index; signaling of low-frequencynon-separable transform (LFNST) index; a joint Cb-Cr mode; or an IntraSubpartition (ISP) mode.
 14. A video processing apparatus, comprising:at least one memory for storing instructions; and at least one processorconfigured to execute the instructions to cause the apparatus toperform: receiving a bitstream comprising a plurality of coding treeunit (CTUs) in a picture; determining whether lossless coding is appliedto the plurality of CTUs, based on a plurality of flags, respectively,wherein the plurality of flags comprise a first flag associated with afirst CTU and each of the plurality of flags is a CTU level losslessflag, and the method further comprises: in response to a determinationthat lossless coding is applied to the first CTU, performing losslesscoding to the first CTU.
 15. A non-transitory computer readable storagemedium storing a set of instructions that are executable by one or moreprocessing devices to cause a video processing apparatus to perform amethod comprising: receiving a bitstream comprising a plurality ofcoding tree unit (CTUs) in a picture; determining whether losslesscoding is applied to the plurality of CTUs, based on a plurality offlags, respectively, wherein the plurality of flags comprise a firstflag associated with a first CTU and each of the plurality of flags is aCTU level lossless flag, and the method further comprises: in responseto a determination that lossless coding is applied to the first CTU,performing lossless coding to the first CTU.
 16. The non-transitorycomputer readable storage medium of claim 15, wherein the set ofinstructions are executable by the one or more processing devices tocause the video processing apparatus to perform: in response to thefirst flag being not signaled in the bitstream, determining that lossycoding is applied to the first CTU.